Modeling Language GNU MathProg

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GNU MathProg Language Reference


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1 Introduction

GNU MathProg is a modeling language intended for describing linear mathematical programming models.1

Model descriptions written in the GNU MathProg language consist of a set of statements and data blocks constructed by the user from the language elements described in this document.

In a process called translation, a program called the model translator analyzes the model description and translates it into internal data structures, which may be then used either for generating mathematical programming problem instance or directly by a program called the solver to obtain numeric solution of the problem.


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1.1 Linear programming problem

In MathProg it is assumed that the linear programming (LP) problem has the following statement:

Minimize (or maximize)
z = c1 x1 + c2 x2 + ... + cn xn + c0

subject to linear constraints

L1 <= a11 x1 + a12 x2 + ... + a1n xn <= U1
L2 <= a21 x1 + a22 x2 + ... + a2n xn <= U2
. . . . .
Lm <= am1 x1 + am2 x2 + ... + amn xn <= Um

and bounds of variables

l1 <= x1 <= u1
l2 <= x2 <= u2
. . . . .
ln <= xn <= un

where:
x1, x2, ..., xn are variables;
z is the objective function;
c1, c2, ..., cn are coefficients of the objective function;
c0 is the constant term (“shift”) of the objective function;
a11, a12, ..., amn are constraint coefficients;
L1, L2, ..., Lm are lower constraint bounds;
U1, U2, ..., Um are upper constraint bounds;
l1, l2, ..., ln are lower bounds of variables;
u1, u2, ..., un are upper bounds of variables.

Bounds of variables and constraint bounds can be finite as well as infinite. Besides, lower bounds can be equal to corresponding upper bounds. Thus, the following types of variables and constraints are allowed:

−inf < x < +inf Free (unbounded) variable
x >= l Variable with lower bound
x <= u Variable with upper bound
l <= x <= u Double-bounded variable
x = l (= u) Fixed variable

−inf < sum aj xj < +inf Free (unbounded) linear form
sum aj xj >= L Inequality constraint “greater than or equal to”
sum aj xj <= U Inequality constraint “less than or equal to”
L <= sum aj xj <= U Double-bounded inequality constraint
sum aj xj = L (= U) Equality constraint

In addition to pure LP problems MathProg allows mixed integer linear programming (MIP) problems, where some (or all) structural variables are restricted to be integer.


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1.2 Model objects

In MathProg the model is described in terms of sets, parameters, variables, constraints, and objectives, which are called model objects.

The user introduces particular model objects using the language statements. Each model object is provided with a symbolic name that uniquely identifies the object and is intended for referencing purposes.

Model objects, including sets, can be multidimensional arrays built over indexing sets. Formally, n-dimensional array A is the mapping:

A : D −> X,

where D within SS... Sn is a subset of the Cartesian product of indexing sets, X is a set of the array members. In MathProg the set D is called subscript domain. Its members are n-tuples (i1, i2, ...in), where iin S1, iin S2, ..., in in Sn.

If n = 0, the Cartesian product above has exactly one element (namely, 0-tuple), so it is convenient to think scalar objects as 0-dimensional arrays which have one member.

The type of array members is determined by the type of corresponding model object as follows:

Model object Array member
Set Elemental plain set
Parameter Number or symbol
Variable Elemental variable
Constraint Elemental constraint
Objective Elemental objective

In order to refer to a particular object member the object should be provided with subscripts. For example, if a is 2-dimensional parameter built over I J, a reference to its particular member can be written as a[ij], where i in I and j in J. It is understood that scalar objects being 0-dimensional need no subscripts.


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1.3 Structure of model description

It is sometimes desirable to write a model which, at various points, may require different data for each problem to be solved using that model. For this reason in MathProg the model description consists of two parts: model section and data section.

Model section is a main part of the model description that contains declarations of model objects and is common for all problems based on the corresponding model.

Data section is an optional part of the model description that contains data specific for a particular problem.

Depending on what is more convenient model and data sections can be placed either in one file or in two separate files. The latter feature allows to have arbitrary number of different data sections to be used with the same model section.


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2 Coding model description

Model description is coded in plain text format using ASCII character set. Valid characters acceptable in the model description are the following:

Within string literals and comments any ASCII characters (except control characters) are valid.

White-space characters are non-significant. They can be used freely between lexical units to improve readability of the model description. They are also used to separate lexical units from each other if there is no other way to do that.

Syntactically model description is a sequence of lexical units in the following categories:

The lexical units of the language are discussed below.


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2.1 Symbolic names

Symbolic name consists of alphabetic and numeric characters, the first of which must be alphabetic. All symbolic names are distinct (case sensitive).

Examples

     alpha123
     This_is_a_name
     _P123_abc_321

Symbolic names are used to identify model objects (sets, parameters, variables, constraints, objectives) and dummy indices.

All symbolic names (except names of dummy indices) must be unique, i.e. the model description must have no objects with the same name. Symbolic names of dummy indices must be unique within the scope, where they are valid.


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2.2 Numeric literals

Numeric literal has the form xxEsyy, where xx is a real number with optional decimal point, s is the sign + or -, yy is an integer decimal exponent. The letter E is case insensitive and can be coded as e.

Examples

     123
     3.14159
     56.E+5
     .78
     123.456e-7

Numeric literals are used to represent numeric quantities. They have obvious fixed meaning.


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2.3 String literals

String literal is a sequence of arbitrary characters enclosed either in single quotes or in double quotes. Both these forms are equivalent.

If the single quote is a part of a string literal enclosed in single quotes, it must be coded twice. Analogously, if the double quote is a part of string literal enclosed in double quotes, it must be coded twice.

Examples

     'This is a string'
     "This is another string"
     '1 + 2 = 3'
     'That''s all'
     "She said: ""No"""

String literals are used to represent symbolic quantities.


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2.4 Keywords

Keyword is a sequence of alphabetic characters and possibly some special characters. All keywords fall into two categories: reserved keywords, which cannot be used as symbolic names, and non-reserved keywords, which being recognized by context can be used as symbolic names.

Reserved keywords are the following:

     and      else     mod      union
     by       if       not      within
     cross    in       or
     diff     inter    symdiff
     div      less     then

Non-reserved keywords are described in following sections.

All the keywords have fixed meaning, which will be explained on discussion of corresponding syntactic constructions, where the keywords are used.


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2.5 Delimiters

Delimiter is either a single special character or a sequence of two special characters as follows:

     +    ^    ==   !    :    )
     -    &    >=   &&   ;    [
     *    <    >    ||   :=   |
     /    <=   <>   .    ..   {
     **   =    !=   ,    (    }

If delimiter consists of two characters, there must be no spaces between the characters.

All the delimiters have fixed meaning, which will be explained on discussion corresponding syntactic constructions, where the delimiters are used.


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2.6 Comments

For documenting purposes the model description can be provided with comments, which have two different forms. The first form is a single-line comment, which begins with the character # and extends until end of line. The second form is a comment sequence, which is a sequence of any characters enclosed between /* and */.

Examples

     set s{1..10}; # This is a comment
     /* This is another comment */

Comments are ignored by the model translator and can appear anywhere in the model description, where white-space characters are allowed.


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3 Expressions

Expression is a rule for computing a value. In model description expressions are used as constituents of certain statements.

In general case expressions consist of operands and operators.

Depending on the type of the resultant value all expressions fall into the following categories:


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3.1 Numeric expressions

Numeric expression is a rule for computing a single numeric value represented in the form of floating-point number.

The primary numeric expression may be a numeric literal, dummy index, unsubscripted parameter, subscripted parameter, built-in function reference, iterated numeric expression, conditional numeric expression, or another numeric expression enclosed in parentheses.

Examples

1.23 (numeric literal)
j (dummy index)
time (unsubscripted parameter)
a['May 2003',j+1] (subscripted parameter)
abs(b[i,j]) (function reference)
sum{i in S diff T} alpha[i] * b[i,j] (iterated expression)
if i in I then 2 * p else q[i+1] (conditional expression)
(b[i,j] + .5 * c) (parenthesized expression)

More general numeric expressions containing two or more primary numeric expressions may be constructed by using certain arithmetic operators.

Examples

     j+1
     2 * a[i-1,j+1] - b[i,j]
     sum{j in J} a[i,j] * x[j] + sum{k in K} b[i,k] * x[k]
     (if i in I then 2 * p else q[i+1]) / (a[i,j] + 1.5)

Numeric literals

If the primary numeric expression is a numeric literal, the resultant value is obvious.

Dummy indices

If the primary numeric expression is a dummy index, the resultant value is current value assigned to the dummy index.

Unsubscripted parameters

If the primary numeric expression is an unsubscripted parameter (which must be 0-dimensional), the resultant value is the value of the parameter.

Subscripted parameters

The primary numeric expression, which refers to a subscripted parameter, has the following syntactic form:

name[i1, i2, ..., in],

where name is the symbolic name of the parameter, i1, i2, ..., in are subscripts.

Each subscript must be a numeric or symbolic expression. The number of subscripts in the subscript list must be the same as the dimension of the parameter with which the subscript list is associated.

Actual values of subscript expressions are used to identify a particular member of the parameter that determines the resultant value of the primary expression.

Function references

In MathProg there are the following built-in functions which may be used in numeric expressions:

abs(x) absolute value
atan(x) trigonometric arctangent arctan x (in radians)
atan(yx) trigonometric arctangent arctan y/x (in radians)
card(x) cardinality (the number of elements) of set x
ceil(x) smallest integer not less than x (“ceiling of x”)
cos(x) trigonometric cosine cos x (in radians)
floor(x) largest integer not greater than x (“floor of x”)
exp(x) base-e exponential e^x
length(x) length of character string x
log(x) natural logarithm log x
log10(x) common (decimal) logarithm log10 x
max(x1, ..., xn) the largest of values x1, ..., xn
min(x1, ..., xn) the smallest of values x1, ..., xn
round(x) rounding x to nearest integer
round(xn) rounding x to n fractional decimal digits
sin(x) trigonometric sine sin x (in radians)
sqrt(x) square root of x
trunc(x) truncating x to nearest integer
trunc(xn) truncating x to n fractional decimal digits
Irand224() pseudo-random integer uniformly distributed in [0,2^24)
Uniform01() pseudo-random number uniformly distributed in [0,1)
Uniform(ab) pseudo-random number uniformly distributed in [ab)
Normal01() Gaussian pseudo-random variate with mu 0 and sigma 1
Normal(mu, sigma) Gaussian pseudo-random variate with given mu and sigma

Arguments of all built-in functions (except card and length) must be numeric expressions. The argument of card must be a set expression. The argument of length must be a symbolic expression.

The resultant value of the numeric expression, which is a function reference, is the result of applying the function to its argument(s).

Note that each pseudo-random generator function have a latent argument (i.e. some internal state), which is changed whenever the function has been applied. Thus, if the function is applied repeatedly even to identical arguments, due to the side effect different resultant values are always produced.

Iterated expressions

Iterated numeric expression is a primary numeric expression, which has the following syntactic form:

iterated-operator indexing-expression integrand

where iterated-operator is the symbolic name of the iterated operator to be performed (see below), indexing expression is an indexing expression which introduces dummy indices and controls iterating, integrand is a numeric expression that participates in the operation.

In MathProg there are four iterated operators, which may be used in numeric expressions:

sum summation of x(i1, ...in) for all (i1, ...inin D
prod production of x(i1, ...in) for all (i1, ...inin D
min minimum of x(i1, ...in) for all (i1, ...inin D
max maximum of x(i1, ...in) for all (i1, ...inin D

where i1, ..., in are dummy indices introduced in the indexing expression, D is the domain, a set of n-tuples specified by the indexing expression which defines particular values assigned to the dummy indices on performing the iterated operation, x(i1, ...in) is the integrand, a numeric expression whose resultant value depends on the dummy indices.

The resultant value of an iterated numeric expression is the result of applying of the iterated operator to its integrand over all n-tuples contained in the domain.

Conditional expressions

Conditional numeric expression is a primary numeric expression, which has one of the following two syntactic forms:

if b then x else y

if b then x

where b is an logical expression, x and y are numeric expressions.

The resultant value of the conditional expression depends on the value of the logical expression that follows the keyword if. If it takes on the value true, the value of the conditional expression is the value of the expression that follows the keyword then. Otherwise, if the logical expression takes on the value false, the value of the conditional expression is the value of the expression that follows the keyword else. If the reduced form of the conditional expression is used and the logical expression takes on the value false, the resultant value of the conditional expression is zero.

Parenthesized expressions

Any numeric expression may be enclosed in parentheses that syntactically makes it primary numeric expression.

Parentheses may be used in numeric expressions, as in algebra, to specify the desired order in which operations are to be performed. Where parentheses are used, the expression within the parentheses is evaluated before the resultant value is used.

The resultant value of the parenthesized expression is the same as the value of the expression enclosed within parentheses.

Arithmetic operators

In MathProg there are the following arithmetic operators, which may be used in numeric expressions:

+ x unary plus
- x unary minus
x + y addition
x - y subtraction
x less y positive difference (if x y then 0 else x − y)
x * y multiplication
x / y division
x div y quotient of exact division
x mod y remainder of exact division
x ** y, x ^ y exponentiation (raise to power)

where x and y are numeric expressions.

If the expression includes more than one arithmetic operator, all operators are performed from left to right according to the hierarchy of operations (see below) with the only exception that the exponentiaion operators are performed from right to left.

The resultant value of the expression, which contains arithmetic operators, is the result of applying the operators to their operands.

Hierarchy of operations

The following list shows the hierarchy of operations in numeric expressions:

Operation Hierarchy
Evaluation of functions (abs, ceil, etc.) 1st
Exponentiation (**, ^) 2nd
Unary plus and minus (+, -) 3rd
Multiplication and division (*, /, div, mod) 4th
Iterated operations (sum, prod, min, max) 5th
Addition and subtraction (+, -, less) 6th
Conditional evaluation (if ... then ... else) 7th

This hierarchy is used to determine which of two consecutive operations is performed first. If the first operator is higher than or equal to the second, the first operation is performed. If it is not, the second operator is compared to the third, etc. When the end of the expression is reached, all of the remaining operations are performed in the reverse order.


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3.2 Symbolic expressions

Symbolic expression is a rule for computing a single symbolic value represented in the form of character string.

The primary symbolic expression may be a string literal, dummy index, unsubscripted parameter, subscripted parameter, built-in function reference, conditional symbolic expression, or another symbolic expression enclosed in parentheses.

It is also allowed to use a numeric expression as the primary symbolic expression, in which case the resultant value of the numeric expression is automatically converted to the symbolic type.

Examples

'May 2003' (string literal)
j (dummy index)
p (unsubscripted parameter)
s['abc',j+1] (subscripted parameter)
substr(name[i],k+1,3) (function reference)
if i in I then s[i,j] else t[i+1] (conditional expression)
((10 * b[i,j]) & '.bis') (parenthesized expression)

More general symbolic expressions containing two or more primary symbolic expressions may be constructed by using the concatenation operator.

Examples

     'abc[' & i & ',' & j & ']'
     "from " & city[i] & " to " & city[j]

The principles of evaluation of symbolic expressions are completely analogous to that ones given for numeric expressions (see above).

Function references

In MathProg there are the following built-in functions which may be used in symbolic expressions:

substr(x, y) substring of x starting from position y
substr(x, y, z) substring of x starting from position y and having length z

The first argument of substr must be a symbolic expression while its second and optional third arguments must be numeric expressions.

The resultant value of the symbolic expression, which is a function reference, is the result of applying the function to its arguments.

Symbolic operators

Currently in MathProg there is the only symbolic operator:

x & y

where x and y are symbolic expressions. This operator means concatenation of its two symbolic operands, which are character strings.

Hierarchy of operations

The following list shows the hierarchy of operations in symbolic expressions:

Operation Hierarchy
Evaluation of numeric operations 1st-7th
Concatenation (&) 8th
Conditional evaluation (if ... then ... else) 9th

This hierarchy has the same meaning as explained in Section “Numeric expressions”.


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3.3 Indexing expressions and dummy indices

Indexing expression is an auxiliary construction, which specifies a plain set of n-tuples and introduces dummy indices. It has two syntactic forms:

{ entry-1, entry-2, ..., entry-m }

{ entry-1, entry-2, ..., entry-m : predicate }

where entry-1, entry-2, ..., entry-m are indexing entries, predicate is a logical expression which specifies an optional predicate.

Each indexing entry in the indexing expression has one of the following three forms:

t in S

(t1, t2, ..., tk) in S

S

where t1, t2, ..., tk are indices, S is a set expression (discussed in the next section), which specifies the basic set.

The number of indices in the indexing entry must be the same as the dimension of the basic set S, i.e. if S consists of 1-tuples, the first form must be used, and if S consists of n-tuples, where n 1, the second form must be used.

If the first form of the indexing entry is used, the index t can be a dummy index only. If the second form is used, the indices t1, t2, ..., tk can be either dummy indices or some numeric or symbolic expressions, where at least one index must be a dummy index. The third, reduced form of the indexing entry has the same effect as if there were t (if S is 1-dimensional) or t1, t2, ..., tk (if S is n-dimensional) all specified as dummy indices.

Dummy index is an auxiliary model object, which acts like an individual variable. Values assigned to dummy indices are components of n-tuples from basic sets, i.e. some numeric and symbolic quantities.

For referencing purposes dummy indices can be provided with symbolic names. However, unlike other model objects (sets, parameters, etc.) dummy indices do not need to be explicitly declared. Each undeclared symbolic name being used in the indexing position of an indexing entry is recognized as the symbolic name of corresponding dummy index.

Symbolic names of dummy indices are valid only within the scope of the indexing expression, where the dummy indices were introduced. Beyond the scope the dummy indices are completely inaccessible, so the same symbolic names may be used for other purposes, in particular, to represent dummy indices in other indexing expressions.

The scope of indexing expression, where implicit declarations of dummy indices are valid, depends on the context, in which the indexing expression is used:

  1. If the indexing expression is used in iterated operator, its scope extends until the end of the integrand.
  2. If the indexing expression is used as a primary set expression, its scope extends until the end of this indexing expression.
  3. If the indexing expression is used to define the subscript domain in declarations of some model objects, its scope extends until the end of the corresponding statement.

The indexing mechanism implemented by means of indexing expressions is best explained by some examples discussed below.

Let there be three sets:

A = {4, 7, 9}

B = {(1,Jan), (1,Feb), (2,Mar), (2,Apr), (3,May), (3,Jun)}

C = {a, b, c}

where A and C consist of 1-tuples (singles), B consists of 2-tuples (doubles). And consider the following indexing expression:

     {i in A, (j,k) in B, l in C}

where i, j, k, and l are dummy indices.

Although MathProg is not a procedural language, for any indexing expression an equivalent algorithmic description could be given. In particular, the algorithmic description of the indexing expression above is the following:

     for all i in A do
        for all (j,k) in B do
           for all l in C do
              action;

where the dummy indices i, j, k, l are consecutively assigned corresponding components of n-tuples from the basic sets A, B, C, and action is some action that depends on the context, where the indexing expression is used. For example, if the action were printing current values of dummy indices, the output would look like follows:

i = 4 j = 1 k = Jan l = a
i = 4 j = 1 k = Jan l = b
i = 4 j = 1 k = Jan l = c
i = 4 j = 1 k = Feb l = a
i = 4 j = 1 k = Feb l = b
... ... ... ...
i = 9 j = 3 k = Jun l = b
i = 9 j = 3 k = Jun l = c

Let the example indexing expression be used in the following iterated operation:

     sum{i in A, (j,k) in B, l in C} p[i,j,k,l]

where p[i, j, k, l] may be a 4-dimensional numeric parameter or some numeric expression whose resultant value depends on i, j, k, and l. In this case the action is summation, so the resultant value of the primary numeric expression is the sum of p[i, j, k, l], where summation is performed over all i in A, (j,kin B, and l in C.

Now let the example indexing expression be used as a primary set expression. In this case the action is gathering all 4-tuples (quadruples) of the form (i, j, k, l) in one set, so the resultant value of such operation is simply the Cartesian product of the basic sets:

A x B x C = {(i,j,k,l) : i in A, (j,kin B, l in C}

Note that in this case the same indexing expression might be written in the reduced form:

     {A, B, C}

because the dummy indices i, j, k, and l are not referenced and therefore their symbolic names are not needed.

Finally, let the example indexing expression be used as the subscript domain in the declaration of a 4-dimensional model object, say, a numeric parameter:

     par p{i in A, (j,k) in B, l in C} ... ;

In this case the action is generating the parameter members, where each member has the form p[ijkl].

As was said above, some indices in the second form of indexing entries may be numeric or symbolic expressions, not only dummy indices. In this case resultant values of such expressions play role of some logical conditions to select only that n-tuples from the Cartesian product of basic sets, which satisfy these conditions.

Consider, for example, the following indexing expression:

     {i in A, (i-1,k) in B, l in C}

where i, k, l are dummy indices, and i−1 is a numeric expression. The algorithmic decsription of this indexing expression is the following:

     for all i in A do
        for all (j,k) in B and j = i-1 do
           for all l in C do
              action;

Thus, if this indexing expression were used as a primary set expression, the resultant set would be the following:

{(4,May,a), (4,May,b), (4,May,c), (4,Jun,a), (4,Jun,b), (4,Jun,c)}.

Should note that in this case the resultant set consists of 3-tuples, not of 4-tuples, because in the indexing expression there is no dummy index that corresponds to the first component of 2-tuples from the set B.

The general rule is: the number of components of n-tuples defined by an indexing expression is the same as the number of dummy indices in that indexing expression, where the correspondence between dummy indices and components on n-tuples in the resultant set is positional, i.e. the first dummy index corresponds to the first component, the second dummy index corresponds to the second component, etc.

In many cases it is needed to select a subset from the Cartesian product of some sets. This may be attained by using an optional logical predicate, which is specified in indexing expression after the last or the only indexing entry.

Consider, for another example, the following indexing expression:

     {i in A, (j,k) in B, l in C: i <= 5 and k <> 'Mar'}

where the logical expression following the colon is a predicate. The algorithmic description of this indexing expression is the following:

     for all i in A do
        for all (j,k) in B do
           for all l in C do
              if i <= 5 and k != 'Mar' then
                 action;

Thus, if this indexing expression were used as a primary set expression, the resultant set would be the following:

{(4,1,Jan,a), (4,1,Feb,a), (4,2,Apr,a), ..., (4,3,Jun,c)}.

If no predicate is specified in the indexing expression, the one, which takes on the value true, is assumed.


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3.4 Set expressions

Set expression is a rule for computing an elemental set, i.e. a collection of n-tuples, where components of n-tuples are numeric and symbolic quantities.

The primary set expression may be a literal set, unsubscripted set, subscripted set, “arithmetic” set, indexing expression, iterated set expression, conditional set expression, or another set expression enclosed in parentheses.

Examples

{(123,'aa'), (i,'bb'), (j-1,'cc')} (literal set)
I (unsubscripted set)
S[i-1,j+1] (subscripted set)
1..t-1 by 2 (“arithmetic” set)
{t in 1..T, (t+1,j) in S: (t,j) in F} (indexing expression)
setof{i in I, j in J}(i+1,j-1) (iterated expression)
if i < j then S[i] else F diff S[j] (conditional expression)
(1..10 union 21..30) (parenthesized expression)

More general set expressions containing two or more primary set expressions may be constructed by using certain set operators.

Examples

     (A union B) inter (I cross J)
     1..10 cross (if i < j then {'a', 'b', 'c'} else {'d', 'e', 'f'})

Literal sets

Literal set is a primary set expression, which has the following two syntactic forms:

{e1, e2, ..., em}

{(e11, ..., e1n), (e21, ..., e2n), ..., (em1, ..., emn)}

where e1, ..., em, e11, ..., emn are numeric or symbolic expressions.

If the first form is used, the resultant set consists of 1-tuples (singles) enumerated within the curly braces. It is allowed to specify an empty set, which has no 1-tuples.

If the second form is used, the resultant set consists of n-tuples enumerated within the curly braces, where a particular n-tuple consists of corresponding components enumerated within the parentheses. All n-tuples must have the same number of components.

Unsubscripted sets

If the primary set expression is an unsubscripted set (which must be 0-dimensional), the resultant set is an elemental set associated with the corresponding set object.

Subscripted sets

The primary set expression, which refers to a subscripted set, has the following syntactic form:

name[i1, i2, ..., in],

where name is the symbolic name of the set object, i1, i2, ..., in are subscripts.

Each subscript must be a numeric or symbolic expression. The number of subscripts in the subscript list must be the same as the dimension of the set object with which the subscript list is associated.

Actual values of subscript expressions are used to identify a particular member of the set object that determines the resultant set.

“Arithmetic” set

The primary set expression, which is an “arithmetic” set, has the following two syntactic forms:

t0 .. tf by dt

t0 .. tf

where t0, t1, and dt are numeric expressions (the value of dt must not be zero). The second form is equivalent to the first form, where dt 1.

If dt 0, the resultant set is determined as follows:

{t: exists k in Z (t = t0 + k dt, t0 <= t <= tf)}

Otherwise, if dt 0, the resultant set is determined as follows:

{t: exists k in Z (t = t0 + k dt, tf <= t <= t0)}

Indexing expressions

If the primary set expression is an indexing expression, the resultant set is determined as described in Section “Indexing expressions and dummy indices” (see above).

Iterated expressions

Iterated set expression is a primary set expression, which has the following syntactic form:

setof indexing-expression integrand

where indexing-expression is an indexing expression which introduces dummy indices and controls iterating, integrand is either a single numeric or symbolic expression or a list of numeric and symbolic expressions separated by commae and enclosed in parentheses.

If the integrand is a single numeric or symbolic expression, the resultant set consists of 1-tuples and is determined as follows:

{x: (i1, ..., in) in D},

where x is a value of the integrand, i1, ..., in are dummy indices introduced in the indexing expression, D is the domain, a set of n-tuples specified by the indexing expression which defines particular values assigned to the dummy indices on performing the iterated operation.

If the integrand is a list containing m numeric and symbolic expressions, the resultant set consists of m-tuples and is determined as follows:

{(x1, ..., xm): (i1, ..., in) in D},

where x1, ..., xm are values of the expressions in the integrand list, i1, ..., in and D have the same meaning as above.

Conditional expressions

Conditional set expression is a primary set expression that has the following syntactic form:

if b then X else Y

where b is an logical expression, X and Y are set expressions, which must define sets of the same dimension.

The resultant value of the conditional expression depends on the value of the logical expression that follows the keyword if. If it takes on the value true, the resultant set is the value of the expression that follows the keyword then. Otherwise, if the logical expression takes on the value false, the resultant set is the value of the expression that follows the keyword else.

Parenthesized expressions

Any set expression may be enclosed in parentheses that syntactically makes it primary set expression.

Parentheses may be used in set expressions, as in algebra, to specify the desired order in which operations are to be performed. Where parentheses are used, the expression within the parentheses is evaluated before the resultant value is used.

The resultant value of the parenthesized expression is the same as the value of the expression enclosed within parentheses.

Set operators

In MathProg there are the following set operators, which may be used in set expressions:

X union Y union
X diff Y difference
X symdiff Y symmetric difference
X inter Y intersection
X cross Y cross (Cartesian) product

where X and Y are set expressions, which must define sets of the identical dimension (except for the Cartesian product).

If the expression includes more than one set operator, all operators are performed from left to right according to the hierarchy of operations (see below).

The resultant value of the expression, which contains set operators, is the result of applying the operators to their operands.

The dimension of the resultant set, i.e. the dimension of n-tuples, of which the resultant set consists of, is the same as the dimension of the operands, except the Cartesian product, where the dimension of the resultant set is the sum of dimensions of the operands.

Hierarchy of operations

The following list shows the hierarchy of operations in set expressions:

Operation Hierarchy
Evaluation of numeric operations 1st-7th
Evaluation of symbolic operations 8th-9th
Evaluation of iterated or “arithmetic” set (setof, ..) 10th
Cartesian product (cross) 11th
Intersection (inter) 12th
Union and difference (union, diff, symdiff) 13th
Conditional evaluation (if ... then ... else) 14th

This hierarchy is used to determine which of two consecutive operations is performed first. If the first operator is higher than or equal to the second, the first operation is performed. If it is not, the second operator is compared to the third, etc. When the end of the expression is reached, all of the remaining operations are performed in the reverse order.


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3.5 Logical expressions

Logical expression is a rule for computing a single logical value, which can be either true or false.

The primary logical expression may be a numeric expression, relational expression, iterated logical expression, or another logical expression enclosed in parentheses.

Examples

i+1 (numeric expression)
a[i,j] < 1.5 (relational expression)
s[i+1,j-1] <> 'Mar' & year (relational expression)
(i+1,'Jan') not in I cross J (relational expression)
S union T within A[i] inter B[j] (relational expression)
forall{i in I, j in J} a[i,j] < .5 * b (iterated expression)
(a[i,j] < 1.5 or b[i] >= a[i,j]) (parenthesized expression)

More general logical expressions containing two or more primary logical expressions may be constructed by using certain logical operators.

Examples

     not (a[i,j] < 1.5 or b[i] >= a[i,j]) and (i,j) in S
     (i,j) in S or (i,j) not in T diff U

Numeric expressions

The resultant value of the primary logical expression, which is a numeric expression, is true, if the resultant value of the numeric expression is non-zero. Otherwise the resultant value of the logical expression is false.

Relational expressions

In MathProg there are the following relational operators, which may be used in logical expressions:

x < y test on x < y
x <= y test on x <= y
x = y, x == y test on x = y
x >= y test on x >= y
x <> y, x != y test on x != y
x in Y test on x in Y
(x1,...,xn) in Y test on (x1,...,xn) in Y
x not in Y, x !in Y test on x not in Y
(x1,...,xn) not in Y,
(x1,...,xn) !in Y test on (x1,...,xn) not in Y
X within Y test on X within Y
X not within Y, X !within Y test on X not within Y

where x, x1, ..., xn, y are numeric or symbolic expressions, X and Y are set expression.

Note:

  1. If x and y are symbolic expressions, only the relational operators =, ==, <>, and != can be used.
  2. In the operations in, not in, and !in the number of components in the first operands must be the same as the dimension of the second operand.
  3. In the operations within, not within, and !within both operands must have identical dimension.

All the relational operators listed above have their conventional mathematical meaning. The resultant value is true, if the corresponding relation is satisfied for its operands, otherwise false.

Iterated expressions

Iterated logical expression is a primary logical expression, which has the following syntactic form:

iterated-operator indexing-expression integrand

where iterated-operator is the symbolic name of the iterated operator to be performed (see below), indexing expression is an indexing expression which introduces dummy indices and controls iterating, integrand is a logical expression that participates in the operation.

In MathProg there are two iterated operators, which may be used in logical expressions:

forall A-quantification for all (i1,...,in) in D: x(i1,...,in)
exists E-quantification exists (i1,...,in) in D: x(i1,...,in)

where i1, ..., in are dummy indices introduced in the indexing expression, D is the domain, a set of n-tuples specified by the indexing expression which defines particular values assigned to the dummy indices on performing the iterated operation, x(i1,...,in) is the integrand, a logical expression whose resultant value depends on the dummy indices.

For A-quantification the resultant value of the iterated logical expression is true, if the value of the integrand is true for all n-tuples contained in the domain, otherwise false.

For E-quantification the resultant value of the iterated logical expression is false, if the value of the integrand is false for all n-tuples contained in the domain, otherwise true.

Parenthesized expressions

Any logical expression may be enclosed in parentheses that syntactically makes it primary logical expression.

Parentheses may be used in logical expressions, as in algebra, to specify the desired order in which operations are to be performed. Where parentheses are used, the expression within the parentheses is evaluated before the resultant value is used.

The resultant value of the parenthesized expression is the same as the value of the expression enclosed within parentheses.

Logical operators

In MathProg there are the following logical operators, which may be used in logical expressions:

not x, ! x negation
x and y, x && y conjunction (logical “and”)
x or y, x || y disjunction (logical “or”)

where x and y are logical expressions.

If the expression includes more than one logical operator, all operators are performed from left to right according to the hierarchy of operations (see below).

The resultant value of the expression, which contains logical operators, is the result of applying the operators to their operands.

Hierarchy of operations

The following list shows the hierarchy of operations in logical expressions:

Operation Hierarchy
Evaluation of numeric operations 1st-7th
Evaluation of symbolic operations 8th-9th
Evaluation of set operations 10th-14th
Relational operations (<, <=, etc.) 15th
Negation (not, !) 16th
Conjunction (and, &&) 17th
A- and E-quantification (forall, exists) 18th
Disjunction (or, ||) 19th

This hierarchy has the same meaning as explained in Section “Numeric expressions”.


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3.6 Linear expressions

Linear expression is a rule for computing so called linear form or simply formula, which is a linear (or affine) function of elemental variables.

The primary linear expression may be an unsubscripted variable, subscripted variable, iterated linear expression, conditional linear expression, or another linear expression enclosed in parentheses.

It is also allowed to use a numeric expression as the primary linear expression, in which case the resultant value of the numeric expression is automatically converted to the formula that includes the only constant term.

Examples

z (unsubscripted variable)
x[i,j] (subscripted variable)
sum{j in J} (a[i] * x[i,j] + 3 * y) (iterated expression)
if i in I then x[i,j] else 1.5 * z + 3 (conditional expression)
(a[i,j] * x[i,j] + y[i-1] + .1) (parenthesized expression)

More general linear expressions containing two or more primary linear expressions may be constructed by using certain arithmetic operators.

Examples

     2 * x[i-1,j+1] + 3.5 * y[k] + .5 * z
     (- x[i,j] + 3.5 * y[k]) / sum{t in T} abs(d[i,j,t])

Unsubscripted variables

If the primary linear expression is an unsubscripted variable (which must be 0-dimensional), the resultant formula is that unsubscripted variable.

Subscripted variables

The primary linear expression, which refers to a subscripted variable, has the following syntactic form:

name[i1, i2, ..., in],

where name is the symbolic name of the variable, i1, i2, ..., in are subscripts.

Each subscript must be a numeric or symbolic expression. The number of subscripts in the subscript list must be the same as the dimension of the variable with which the subscript list is associated.

Actual values of subscript expressions are used to identify a particular member of the model variable that determines the resultant formula, which is an elemental variable associated with the corresponding member.

Iterated expressions

Iterated linear expression is a primary linear expression, which has the following syntactic form:

sum indexing-expression integrand

where indexing-expression is an indexing expression which introduces dummy indices and controls iterating, integrand is a linear expression that participates in the operation.

The iterated linear expression is evaluated exactly in the same way as the iterated numeric expression (see Section “Numeric expressions” above) with the exception that the integrand participated in the summation is a formula, not a numeric value.

Conditional expressions

Conditional linear expression is a primary linear expression, which has one of the following two syntactic forms:

if b then f else g

if b then f

where b is an logical expression, f and g are linear expressions.

The conditional linear expression is evaluated exactly in the same way as the conditional numeric expression (see Section “Numeric expressions” above) with the exception that operands participated in the operation are formulae, not numeric values.

Parenthesized expressions

Any linear expression may be enclosed in parentheses that syntactically makes it primary linear expression.

Parentheses may be used in linear expressions, as in algebra, to specify the desired order in which operations are to be performed. Where parentheses are used, the expression within the parentheses is evaluated before the resultant formula is used.

The resultant value of the parenthesized expression is the same as the value of the expression enclosed within parentheses.

Arithmetic operators

In MathProg there are the following arithmetic operators, which may be used in linear expressions:

+ f unary plus
- f unary minus
f + g addition
f - g subtraction
x * f, f * x multiplication
f / x division

where f and g are linear expressions, x is a numeric expression (more precisely, a linear expression containing the constant term only).

If the expression includes more than one arithmetic operator, all operators are performed from left to right according to the hierarchy of operations (see below).

The resultant value of the expression, which contains arithmetic operators, is the result of applying the operators to their operands.

Hierarchy of operations

The hierarchy of arithmetic operations used in linear expressions is the same as for numeric expressions (for details see Section “Numeric expressions” above).


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4 Statements

Statements are basic units of the model description. In MathProg all statements are divided into two categories: declaration statements and functional statements.

Declaration statements (set statement, parameter statement, variable statement, constraint statement, and objective statement) are used to declare model objects of certain kinds and define certain properties of that objects.

Functional statements (solve statement, check statement, display statement, printf statement, loop statement) are intended for performing some specific actions.

Note that declaration statements may follow in arbitrary order which does not affect the result of translation. However, any model object must be declared before it is referenced in other statements.


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4.1 Set statement

set name alias domain , attrib , ... , attrib ;

Where:
name is the symbolic name of the set;
alias is an optional string literal which specifies the alias of the set;
domain is an optional indexing expression which specifies the subscript domain of the set;
attrib, ..., attrib are optional attributes of the set. (Commae preceding attributes may be omitted.)

Optional attributes:

dimen n
specifies dimension of n-tuples, which the set consists of;
within expression
specifies a superset which restricts the set or all its members (elemental sets) to be within this superset;
:= expression
specifies an elemental set assigned to the set or its members;
default expression
specifies an elemental set assigned to the set or its members whenever no appropriate data are available in the data section.

Examples

     set V;
     set E within V cross V;
     set step{s in 1..maxiter} dimen 2 := if s = 1 then E else step[s-1]
        union setof{k in V, (i,k) in step[s-1], (k,j) in step[s-1]}(i,j);
     set A{i in I, j in J}, within B[i+1] cross C[j-1], within D diff E,
        default {('abc',123), (321,'cba')};

The set statement declares a set. If the subscript domain is not specified, the set is a simple set, otherwise it is an array of elemental sets.

The dimen attribute specifies dimension of n-tuples, which the set (if it is a simple set) or its members (if the set is an array of elemental sets) consist of, where n must be unsigned integer from 1 to 20. At most one dimen attribute can be specified. If the dimen attribute is not specified, dimension of n-tuples is implicitly determined by other attributes (for example, if there is a set expression that follows := or the keyword default, the dimension of n-tuples of the corresponding elemental set is used). If no dimension information is available, dimen 1 is assumed.

The within attribute specifies a set expression whose resultant value is a superset used to restrict the set (if it is a simple set) or its members (if the set is an array of elemental sets) to be within this superset. Arbitrary number of within attributes may be specified in the same set statement.

The assign (:=) attribute specifies a set expression used to evaluate elemental set(s) assigned to the set (if it is a simple set) or its members (if the set is an array of elemental sets). If the assign attribute is specified, the set is computable and therefore needs no data to be provided in the data section. If the assign attribute is not specified, the set must be provided with data in the data section. At most one assign or default attribute can be specified for the same set.

The default attribute specifies a set expression used to evaluate elemental set(s) assigned to the set (if it is a simple set) or its members (if the set is an array of elemental sets) whenever no appropriate data are available in the data section. If neither assign nor default attribute is specified, missing data will cause an error.


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4.2 Parameter statement

param name alias domain , attrib , ... , attrib ;

Where:
name is the symbolic name of the parameter;
alias is an optional string literal which specifies the alias of the parameter;
domain is an optional indexing expression which specifies the subscript domain of the parameter;
attrib, ..., attrib are optional attributes of the parameter. (Commae preceding attributes may be omitted.)

Optional attributes:

integer
specifies that the parameter is integer;
binary
specifies that the parameter is binary;
symbolic
specifies that the parameter is symbolic;
relation expression
(where relation is one of: < <= = == >= > <> !=)
specifies a condition that restricts the parameter or its members to satisfy this condition;
in expression
specifies a superset that restricts the parameter or its members to be in this superset;
:= expression
specifies a value assigned to the parameter or its members;
default expression
specifies a value assigned to the parameter or its members whenever no appropriate data are available in the data section.

Examples

     param units{raw, prd} >= 0;
     param profit{prd, 1..T+1};
     param N := 20, integer, >= 0, <= 100;
     param comb 'n choose k' {n in 0..N, k in 0..n} :=
        if k = 0 or k = n then 1 else comb[n-1,k-1] + comb[n-1,k];
     param p{i in I, j in J}, integer, >= 0, <= i+j, in A[i] symdiff B[j],
        in C[i,j], default 0.5 * (i + j);
     param month symbolic default 'May' in {'Mar', 'Apr', 'May'};

The parameter statement declares a parameter. If the subscript domain is not specified, the parameter is a simple (scalar) parameter, otherwise it is a n-dimensional array.

The type attributes integer, binary, and symbolic qualify the type values which can be assigned to the parameter as shown below:

Type attribute Assigned values
not specified Any numeric values
integer Only integer numeric values
binary Either 0 or 1
symbolic Any numeric and symbolic values

The symbolic attribute cannot be specified along with other type attributes. Being specified it must precede all other attributes.

The condition attribute specifies an optional condition that restricts values assigned to the parameter to satisfy this condition. This attribute has the following syntactic forms:

< v Check for x < v
<= v Check for x <= v
= v, == v Check for x = v
>= v Check for x >= v
> v Check for x > v
<> v, != v Check for x != v

where x is a value assigned to the parameter, v is the resultant value of a numeric or symbolic expression specified in the condition attribute. If the parameter is symbolic, conditions in the form of inequality are not allowed. Arbitrary number of condition attributes can be specified for the same parameter. If a value being assigned to the parameter during model evaluation violates at least one specified condition, an error is raised.

The in attribute is similar to the condition attribute and specifies a set expression whose resultant value is a superset used to restrict numeric or symbolic values assigned to the parameter to be in this superset. Arbitrary number of the in attributes can be specified for the same parameter. If a value being assigned to the parameter during model evaluation is not in at least one specified superset, an error is raised.

The assign (:=) attribute specifies a numeric or symbolic expression used to compute a value assigned to the parameter (if it is a simple parameter) or its member (if the parameter is an array). If the assign attribute is specified, the parameter is computable and therefore needs no data to be provided in the data section. If the assign attribute is not specified, the parameter must be provided with data in the data section. At most one assign or default attribute can be specified for the same parameter.

The default attribute specifies a numeric or symbolic expression used to compute a value assigned to the parameter or its member whenever no appropriate data are available in the data section. If neither assign nor default attribute is specified, missing data will cause an error.


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4.3 Variable statement

var name alias domain , attrib , ... , attrib ;

Where:
name is the symbolic name of the variable;
alias is an optional string literal which specifies the alias of the variable;
domain is an optional indexing expression which specifies the subscript domain of the variable;
attrib, ..., attrib are optional attributes of the variable. (Commae preceding attributes may be omitted.)

Optional attributes:

integer
restricts the variable to be integer;
binary
restricts the variable to be binary;
>= expression
specifies an lower bound of the variable;
<= expression
specifies an upper bound of the variable;
= expression, == expression
specifies a fixed value of the variable;

Examples

     var x >= 0;
     var y{I,J};
     var make{p in prd}, integer, >= commit[p], <= market[p];
     var store{raw, 1..T+1} >= 0;
     var z{i in I, j in J} >= i+j;

The variable statement declares a variable. If the subscript domain is not specified, the variable is a simple (scalar) variable, otherwise it is a n-dimensional array of elemental variables.

Elemental variable(s) associated with the model variable (if it is a simple variable) or its members (if it is an array) correspond to the variables in the LP/MIP problem formulation (see Section “Linear programming problem”). Note that only the elemental variables actually referenced in some constraints and/or objectives are included in the LP/MIP problem instance to be generated.

The type attributes integer and binary restrict the variable to be integer or binary, respectively. If no type attribute is specified, the variable is continuous. If all variables in the model are continuous, the corresponding problem is of LP class. If there is at least one integer or binary variable, the problem is of MIP class.

The lower bound (>=) attribute specifies a numeric expression for computing the lower bound of the variable. At most one lower bound can be specified. By default all variables (except binary ones) have no lower bounds, so if a variable is required to be non-negative, its zero lower bound should be explicitly specified.

The upper bound (<=) attribute specifies a numeric expression for computing the upper bound of the variable. At most one upper bound attribute can be specified.

The fixed value (=) attribute specifies a numeric expression for computing the value, at which the variable is fixed. This attribute cannot be specified along with lower/upper bound attributes.


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4.4 Constraint statement

subject to name alias domain : expression , = expression ;

subject to name alias domain : expression , <= expression ;

subject to name alias domain : expression , >= expression ;

subject to name alias domain : expression , <= expression , <= expression ;

subject to name alias domain : expression , >= expression , >= expression ;

Where:
name is the symbolic name of the constraint;
alias is an optional string literal which specifies the alias of the constraint;
domain is an optional indexing expression which specifies the subscript domain of the constraint;
expressions are linear expressions for computing components of the constraint. (Commae following expressions may be omitted.)
Note:
The keyword subject to may be reduced to subj to, or to s.t., or be omitted at all.

Examples

     s.t. r: x + y + z, >= 0, <= 1;
     limit{t in 1..T}: sum{j in prd} make[j,t] <= max_prd;
     subject to balance{i in raw, t in 1..T}:
        store[i,t+1] - store[i,t] - sum{j in prd} units[i,j] * make[j,t];
     subject to rlim 'regular-time limit' {t in time}:
        sum{p in prd} pt[p] * rprd[p,t] <= 1.3 * dpp[t] * crews[t];

The constraint statement declares a constraint. If the subscript domain is not specified, the constraint is a simple (scalar) constraint, otherwise it is a n-dimensional array of elemental constraints.

Elemental constraint(s) associated with the model constraint (if it is a simple constraint) or its members (if it is an array) correspond to the linear constraints in the LP/MIP problem formulation (see Section “Linear programming problem”).

If the constraint has the form of equality or single inequality, i.e. includes two expressions, one of which follows the colon and other follows the relation sign =, <=, or >=, both expressions in the statement can be linear expressions. If the constraint has the form of double inequality, i.e. includes three expressions, the middle expression can be a linear expression while the leftmost and rightmost ones can be only numeric expressions.

Generating the model is, generally speaking, generating its constraints, which are always evaluated for the entire subscript domain. Evaluating constraints leads, in turn, to evaluating other model objects such as sets, parameters, and variables.

Constructing the actual linear constraint included in the problem instantce, which (constraint) corresponds to a particular elemental constraint, is performed as follows.

If the constraint has the form of equality or single inequality, evaluation of both linear expressions gives two resultant linear forms:

f = a1 x1 + a2 x2 + ... + an xn + a0,

g = b1 x1 + b2 x2 + ... + bn xn + b0,

where x1, x2, ..., xn are elemental variables, a1, a2, ..., an, b1, b2, ..., bn are numeric coefficients, a0 and b0 are constant terms. Then all linear terms of f and g are carried to the left-hand side, and the constant terms are carried to the right-hand side that gives the final elemental constraint in the standard form:

(a1 − b1) x1 + (a2 − b2) x2 + ... + (anbn) xn {= | <= | =>} b0 − a0

If the constraint has the form of double inequality, evaluation of the middle linear expression gives the resultant linear form:

f = a1 x1 + a2 x2 + ... + an xn + a0,

and evaluation of the leftmost and rightmost numeric expressions gives two numeric values l and u. Then the constant term of the linear form is carried to both left-hand and right-hand sides that gives the final elemental constraint in the standard form:

la0 <= a1 x1 + a2 x2 + ... + an xn <= ua0.


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4.5 Objective statement

minimize name alias domain : expression ;

maximize name alias domain : expression ;

Where:
name is the symbolic name of the objective;
alias is an optional string literal which specifies the alias of the objective;
domain is an optional indexing expression which specifies the subscript domain of the objective;
expression is an linear expression for computing the linear form of the objective

Examples

     minimize obj: x + 1.5 * (y + z);
     maximize total_profit: sum{p in prd} profit[p] * make[p];

The objective statement declares an objective. If the subscript domain is not specified, the objective is a simple (scalar) objective. Otherwise it is a n-dimensional array of elemental objectives.

Elemental objective(s) associated with the model objective (if it is a simple objective) or its members (if it is an array) correspond to general linear constraints in the LP/MIP problem formulation (see Section “Linear programming problem”). However, unlike constraints the corresponding linear forms are free (unbounded).

Constructing the actual linear constraint included in the problem instance, which (constraint) corresponds to a particular elemental objective, is performed as follows. The linear expression specified in the objective statement is evaluated that gives the resultant linear form:

f = a1 x1 + a2 x2 + ... + an xn + a0,

where x1, x2, ..., xn are elemental variables, a1, a2, ..., an are numeric coefficients, a0 is the constant term. Then the linear form is used to construct the final elemental constraint in the standard form:

−inf < a1 x1 + a2 x2 + ... + an xn + a0 < +inf.

As a rule the model description contains only one objective statement that defines the objective function (1) used in the problem instance. However, it is allowed to declare arbitrary number of objectives, in which case the actual objective function is the first objective encountered in the model description. Other objectives are also included in the problem instance, but they do not affect the objective function.


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4.6 Solve statement

solve ;

Note:
The solve statement is optional and can be used only once. If no solve statement is used, one is assumed at the end of the model section.

The solve statement causes solving the model, i.e. computing numeric values of all model variables. This allows using variables in statements below the solve statement in the same way as if they were numeric parameters.

Note that variable, constraint, and objective statements cannot be used below the solve statement, i.e. all principal components of the model must be described above the solve statement.


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4.7 Check statement

check domain : expression ;

Where:
domain is an optional indexing expression which specifies the subscript domain of the check statement;
expression is an logical expression which specifies the logical condition to be checked. (The colon preceding expression may be omitted.)

Examples

     check: x + y <= 1 and x >= 0 and y >= 0;
     check sum{i in ORIG} supply[i] = sum{j in DEST} demand[j];
     check{i in I, j in 1..10}: S[i,j] in U[i] union V[j];

The check statement allows checking the resultant value of an logical expression specified in the statement. If the value is false, the model translator reports an error.

If the subscript domain is not specified, the check is performed only once. Specifying the subscript domain allows performing multiple checks for every n-tuple in the domain set. In the latter case the logical expression may include dummy indices introduced in the corresponding indexing expression.


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4.8 Display statement

display domain : item , ... , item ;

Where:
domain is an optional indexing expression which specifies the subscript domain of the display statement;
item, ..., item are items to be displayed. (The colon preceding the first item may be omitted.)

Examples

     display: 'x =', x, 'y =', y, 'z =', z;
     display sqrt(x ** 2 + y ** 2 + z ** 2);
     display{i in I, j in J}: i, j, a[i,j], b[i,j];

The display statement evaluates all items specified in the statement and writes their values to the terminal in plain text format.

If the subscript domain is not specified, items are evaluated and then displayed only once. Specifying the subscript domain causes evaluating and displaying items for every n-tuple in the domain set. In the latter case items may include dummy indices introduced in the corresponding indexing expression.

Item to be displayed can be a model object (set, parameter, variable, constraint, objective) or an expression.

If the item is a computable object (i.e. a set or parameter provided with the assign attribute), the object is evaluated over the entire domain and then its content (i.e. the content of the object array) is displayed. Otherwise, if the item is not a computable object, only its current content (i.e. the members actually generated during the model evaluation) is displayed. Note that if the display statement is used above the solve statement and the item is a variable, its displayed “value” means “elemental variable”, not a numeric value, which the variable could have in some solution obtained by the solver. To display a numeric value of a variable the display statement should be used below the solve statement. Analogously, if the item is a constraint or objective, its “value” means “elemental constraint” or “elemental objective”, not a numeric value.

If the item is an expression, the expression is evaluated and its resultant value is displayed.


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4.9 Printf statement

printf domain : format , expression , ... , expression ;

printf domain : format , expression , ... , expression > filename ;

printf domain : format , expression , ... , expression >> filename ;

Where:
domain is an optional indexing expression which specifies the subscript domain of the printf statement;
format is a symbolic expression whose value specifies a format control string. (The colon preceding the format expression may be omitted.)
expression, ..., expression are zero or more expressions whose values have to be formatted and printed. Each expression must be of numeric, symbolic, or logical type.
filename is a symbolic expression whose value specifies the name of a text file, to which the printf output should be redirected. The flag > means creating a new empty file while the flag >> means appending the output to an existing file. If no file name is specified, the output is written to the terminal.

Examples

     printf 'Hello, world!\n';
     printf: "x = %.3f; y = %.3f; z = %.3f\n", x, y, z > "result.txt";
     printf{i in I, j in J}: "flow from %s to %s is %d\n", i, j, x[i,j];
     printf{i in I} 'total flow from %s is %g\n', i, sum{j in J} x[i,j];
     printf{k in K} "x[%s] = " & (if x[k] < 0 then "?" else "%g"), k, x[k];

The printf statement is similar to the display statement, however, it allows formatting the data to be written.

If the subscript domain is not specified, the printf statement is executed only once. Specifying the subscript domain causes executing the printf statement for every n-tuple in the domain set. In the latter case format and expressions may include dummy indices introduced in the corresponding indexing expression.

The format control string is a value of the symbolic expression format specified in the printf statement. It is composed of zero or more directives as follows: ordinary characters (not %), which are copied unchanged to the output stream, and conversion specifications, each of which causes evaluating corresponding expression specified in the printf statement, formatting it, and writing the resultant value to the output stream.

Conversion specifications which may be used in the format control string are the following: d, i, f, F, e, E, g, G, and s. These specifications have the same syntax and semantics as in the C programming language.


Previous: Printf statement, Up: Statements

4.10 For statement

for domain : statement

for domain : { statement ... statement }

Where:
domain is an indexing expression which specifies the subscript domain of the for statement. (The colon following the indexing expression may be omitted.)
statement is a statement which should be executed under control of the for statement;
statement, ..., statement is a sequence of statements (enclosed in curly braces) which should be executed under control of the for statement.
Note:
Only the following statements are allowed within the for statement: check, display, printf, and another for.

Examples

     for {(i,j) in E: i != j}
     {  printf "flow from %s to %s is %g\n", i, j, x[i,j];
        check x[i,j] >= 0;
     }
     for {i in 1..n}
     {  for {j in 1..n} printf " %s", if x[i,j] then "Q" else ".";
        printf("\n");
     }
     for {1..72} printf("*");

The for statement causes executing a statement or a sequence of statements specified as part of the for statement for every n-tuple in the domain set. Thus, statements within the for statement may refer to dummy indices introduced in the corresponding indexing expression.


Next: , Previous: Statements, Up: Top

5 Model data

Model data include elemental sets, which are “values” of model sets, and numeric and symbolic values of model parameters.

In MathProg there are two different ways to saturate model sets and parameters with data. One way is simply providing necessary data using the assign attribute. However, in many cases it is more practical to separate the model itself and particular data needed for the model. For the latter reason in MathProg there is other way, when the model description is divided into two parts: model section and data section.

Model section is a main part of the model description that contains declarations of all model objects and is common for all problems based on that model.

Data section is an optional part of the model description that contains model data specific for a particular problem.

In MathProg model and data sections can be placed either in one text file or in two separate text files.

If both model and data sections are placed in one file, the file is composed as follows:

     +------------+
     | statement  |
     | statement  |
     | . . .      |
     | statement  |
     | data;      |
     | data block |
     | data block |
     | . . .      |
     | data block |
     | end;       |
     +------------+

If the model and data sections are placed in two separate files, the files are composed as follows:

     +------------+   +------------+
     | statement  |   | data;      |
     | statement  |   | data block |
     | . . .      |   | data block |
     | statement  |   | . . .      |
     | end;       |   | data block |
     |            |   | end;       |
     +------------+   +------------+
       Model file       Data file
Note:
If the data section is placed in a separate file, the keyword data is optional and may be omitted along with the semicolon that follows it.


Next: , Up: Model data

5.1 Coding data section

The data section is a sequence of data blocks in various formats, which are discussed in following subsections. The order, in which data blocks follow in the data section, may be arbitrary, not necessarily the same as in which the corresponding model objects follow in the model section.

The rules of coding the data section are commonly the same as the rules of coding the model description (for details see Section “Coding model description”), i.e. data blocks are composed from basic lexical units such as symbolic names, numeric and string literals, keywords, delimiters, and comments. However, for the sake of convenience and improving readability there is one deviation from the common rule: if a string literal consists of only alphanumeric characters (including the underscore character), the signs + and -, and/or the decimal point, it may be coded without bordering (single or double) quotes.

All numeric and symbolic material provided in the data section is coded in the form of numbers and symbols, i.e. unlike the model section no expressions are allowed in the data section. Nevertheless the signs + and - can precede numeric literals to allow coding signed numeric quantities, in which case there must be no white-space characters between the sign and following numeric literal (if there is at least one white-space, the sign and following numeric literal are recognized as two different lexical units).


Next: , Previous: Coding data section, Up: Model data

5.2 Set data block

set name , record , ... , record ;

set name [ symbol , ... , symbol ] , record , ... , record ;

Where:
name is a symbolic name of the set;
symbol, ..., symbol are subscripts which specify a particular member of the set (if the set is an array, i.e. a set of sets);
record, ..., record are data records.
Note:
Commae preceding data records may be omitted.

Data records:

:=
is a non-significant data record which may be used freely to improve readability;
( slice )
specifies a slice;
simple-data
specifies set data in the simple format;
: matrix-data
specifies set data in the matrix format;
(tr) : matrix-data
specifies set data in the transposed matrix format. (In this case the colon following the keyword (tr) may be omitted.)

Examples

     set month := Jan Feb Mar Apr May Jun;
     set month "Jan", "Feb", "Mar", "Apr", "May", "Jun";
     set A[3,Mar] := (1,2) (2,3) (4,2) (3,1) (2,2) (4,4) (3,4);
     set A[3,'Mar'] := 1 2 2 3 4 2 3 1 2 2 4 4 2 4;
     set A[3,'Mar'] : 1 2 3 4 :=
                    1 - + - -
                    2 - + + -
                    3 + - - +
                    4 - + - + ;
     set B := (1,2,3) (1,3,2) (2,3,1) (2,1,3) (1,2,2) (1,1,1) (2,1,1);
     set B := (*,*,*) 1 2 3, 1 3 2, 2 3 1, 2 1 3, 1 2 2, 1 1 1, 2 1 1;
     set B := (1,*,2) 3 2 (2,*,1) 3 1 (1,2,3) (2,1,3) (1,1,1);
     set B := (1,*,*) : 1 2 3 :=
                      1 + - -
                      2 - + +
                      3 - + -
              (2,*,*) : 1 2 3 :=
                      1 + - +
                      2 - - -
                      3 + - - ;

(In these examples the set month is a simple set of singles, A is a 2-dimensional array of doubles, and B is a simple set of triples. Data blocks for the same set are equivalent in the sense that they specify the same data in different formats.)

The set data block is used to specify a complete elemental set, which is assigned to a set (if it is a simple set) or one of its members (if the set is an array of sets).2

Data blocks can be specified only for non-computable sets, i.e. sets which have no assign attribute in the corresponding set statements.

If the set is a simple set, only its symbolic name should be given in the header of the data block. Otherwise, if the set is a n-dimensional array, its symbolic name should be provided with a complete list of subscripts separated by commae and enclosed in square brackets to specify a particular member of the set array. The number of subscripts must be the same as the dimension of the set array, where each subscript must be a number or symbol.

The elemental set defined in the set data block is coded as a sequence of data records described below.3

Assign data record

The assign (:=) data record is a non-signficant element. It may be used for improving readability of data blocks.

Slice data record

The slice data record is a control record which specifies a slice of the elemental set defined in the data block. It has the following syntactic form:

( s1 , s2 , ... , sn )

where s1, s2, ..., sn are components of the slice.

Each component of the slice can be a number or symbol or the asterisk (*). The number of components in the slice must be the same as the dimension of n-tuples in the elemental set to be defined. For instance, if the elemental set contains 4-tuples (quadruples), the slice must have four components. The number of asterisks in the slice is called slice dimension.

The effect of using slices is the following. If a m-dimensional slice (i.e. a slice which has m asterisks) is specified in the data block, all subsequent data records must specifiy tuples of the dimension m. Whenever a m-tuple is encountered, each asterisk in the slice is replaced by corresponding components of the m-tuple that gives the resultant n-tuple, which is included in the elemental set to be defined. For example, if the slice (a,*,1,2,*) is in effect, and 2-tuple (3,b) is encountered in a subsequent data record, the resultant 5-tuple included in the elemental set is (a,3,1,2,b).

The slice that has no asterisks itself defines a complete n-tuple, which is included in the elemental set.

Being once specified the slice effects until either a new slice or the end of data block has been encountered. Note that if there is no slice specified in the data block, a dummy one, components of which are all asterisks, is assumed.

Simple data record

The simple data record defines one n-tuple in simple format and has the following syntactic form:

t1 , t2 , ... , tn

where t1, t2, ..., tn are components of the n-tuple. Each component can be a number or symbol. Commae between components are optional and may be omitted.

Matrix data record

The matrix data record defines several 2-tuples (doubles) in matrix format and has the following syntactic form:

: c1 c2 ... cn :=
r1 a11 a12 ... a1n
r2 a21 a22 ... a2n
... ... ... ... ...
rm am1 am2 ... amn

where r1, r2, ..., rm are numbers and/or symbols which correspond to rows of the matrix, c1, c2, ..., cn are numbers and/or symbols which correspond to columns of the matrix, a11, a12, ..., amn are the matrix elements, which can be either the sign + or the sign -. (In this data record the delimiter : preceding the column list and the delimiter := following the column list cannot be omitted.)

Each element aij of the matrix data block (where 1 <= <= m, 1 <= <= n) corresponds to 2-tuple (ricj). If aij is the plus sign (+), the corresponding 2-tuple (or a longer n-tuple, if a slice is used) is included in the elemental set. Otherwise, if aij is the minus sign (-) sign, the corresponding 2-tuple is not included in the elemental set.

Since the matrix data record defines 2-tuples, either the elemental set must consist of 2-tuples or the slice currently used must be 2-dimensional.

Transposed matrix data record

The transposed matrix data record has the following syntactic form:

(tr) : c1 c2 ... cn :=
r1 a11 a12 ... a1n
r2 a21 a22 ... a2n
... ... ... ... ...
rm am1 am2 ... amn

(In this case the delimiter : following the keyword (tr) is optional and may be omitted.)

This data record is completely analogous to the matrix data record (see above) with the only exception that each element aij of the matrix corresponds to 2-tuple (cjri).

Being once specified the (tr) indicator effects on all subsequent data records until either a slice or the end of data block has been encountered.


Previous: Set data block, Up: Model data

5.3 Parameter data block

param name , record , ... , record ;

param name default value , record , ... , record ;

param : tabbing-data ;

param default value : tabbing-data ;

Where:
name is a symbolic name of the parameter;
value is an optional default value of the parameter;
record, ..., record are data records.
tabbing-data specifies parameter data in the tabbing format.
Note:
Commae preceding data records may be omitted.

Data records:

:=
is a non-significant data record which may be used freely to improve readability;
[ slice ]
specifies a slice;
plain-data
specifies parameter data in the plain format;
: tabular-data
specifies parameter data in the tabular format;
(tr) : tabular-data
specifies parameter data in the transposed tabular format. (In this case the colon following the keyword (tr) may be omitted.)

Examples

     param T := 4;
     param month := 1 Jan 2 Feb 3 Mar 4 Apr 5 May;
     param month := [1] 'Jan', [2] 'Feb', [3] 'Mar', [4] 'Apr', [5] 'May';
     param init_stock := iron 7.32 nickel 35.8;
     param init_stock [*] iron 7.32, nickel 35.8;
     param cost [iron] .025 [nickel] .03;
     param value := iron -.1, nickel .02;
     param       : init_stock  cost  value :=
           iron       7.32     .025   -.1
           nickel    35.8      .03     .02 ;
     param : raw : init stock  cost  value :=
             iron     7.32     .025   -.1
             nickel  35.8      .03     .02 ;
     param demand default 0 (tr)
            :  FRA  DET  LAN  WIN  STL  FRE  LAF :=
        bands  300   .   100   75   .   225  250
        coils  500  750  400  250   .   850  500
        plate  100   .    .    50  200   .   250 ;
     param trans_cost :=
        [*,*,bands]:  FRA  DET  LAN  WIN  STL  FRE  LAF :=
              GARY     30   10    8   10   11   71    6
              CLEV     22    7   10    7   21   82   13
              PITT     19   11   12   10   25   83   15
        [*,*,coils]:  FRA  DET  LAN  WIN  STL  FRE  LAF :=
              GARY     39   14   11   14   16   82    8
              CLEV     27    9   12    9   26   95   17
              PITT     24   14   17   13   28   99   20
        [*,*,plate]:  FRA  DET  LAN  WIN  STL  FRE  LAF :=
              GARY     41   15   12   16   17   86    8
              CLEV     29    9   13    9   28   99   18
              PITT     26   14   17   13   31  104   20 ;

The parameter data block is used to specify complete data for a parameter (or parameters, if data are specified in the tabbing format) whose name is given in the block.

Data blocks can be specified only for the parameters, which are non-computable, i.e. which have no assign attribute in the corresponding parameter statements.

Data defined in the parameter data block are coded as a sequence of data records described below. Additionally the data block can be provided with the optional default attribute, which specifies a default numeric or symbolic value of the parameter (parameters). This default value is assigned to the parameter or its members, if no appropriate value is defined in the parameter data block. The default attribute cannot be used, if it is already specified in the corresponding parameter statement(s).

Assign data record

The assign (:=) data record is a non-signficant element. It may be used for improving readability of data blocks.

Slice data record

The slice data record is a control record which specifies a slice of the parameter array. It has the following syntactic form:

[ s1 , s2 , ... , sn ]

where s1, s2, ..., sn are components of the slice.

Each component of the slice can be a number or symbol or the asterisk (|*|). The number of components in the slice must be the same as the dimension of the parameter. For instance, if the parameter is a 4-dimensional array, the slice must have four components. The number of asterisks in the slice is called slice dimension.

The effect of using slices is the following. If a m-dimensional slice (i.e. a slice which has m asterisks) is specified in the data block, all subsequent data records must specify subscripts of the parameter members as if the parameter were m-dimensional, not n-dimensional.

Whenever m subscripts are encountered, each asterisk in the slice is replaced by corresponding subscript that gives n subscripts, which define the actual parameter member. For example, if the slice [a,*,1,2,*] is in effect, and the subscripts 3 and b are encountered in a subsequent data record, the complete subscript list used to choose a parameter member is [a,3,1,2,b].

It is allowed to specify a slice that has no asterisks. Such slice itself defines a complete subscript list, in which case the next data record can define only a single value of the corresponding parameter member.

Being once specified the slice effects until either a new slice or the end of data block has been encountered. Note that if there is no slice specified in the data block, a dummy one, components of which are all asterisks, is assumed.

Plain data record

The plain data record defines the subscript list and a single value in plain format. This record has the following syntactic form:

t1 , t2 , ... , tn , v

where t1, t2, ..., tn are subscripts, v is a value. Each subscript as well as the value can be a number or symbol. Commae following subscripts are optional and may be omitted.

In case of 0-dimensional parameter or slice the plain data record have no subscripts and consists of a single value only.

Tabular data record

The tabular data record defines several values, where each value is provided with two subscripts. This record has the following syntactic form:

: c1 c2 ... cn :=
r1 a11 a12 ... a1n
r2 a21 a22 ... a2n
... ... ... ... ...
rm am1 am2 ... amn

where r1, r2, ..., rm are numbers and/or symbols which correspond to rows of the table, c1, c2, ..., cn are numbers and/or symbols which correspond to columns of the table, a11, a12, ..., amn are the table elements. Each element can be a number or symbol or the single decimal point. (In this data record the delimiter : preceding the column list and the delimiter := following the column list cannot be omitted.)

Each element aij of the tabular data block (1 <= <= m, 1 <= <= n) defines two subscripts, where the first subscript is ri, and the second one is cj. These subscripts are used in conjunction with the current slice to form the complete subscript list which identifies a particular member of the parameter array. If aij is a number or symbol, this value is assigned to the parameter member. However, if aij is the single decimal point, the member is assigned a default value specified either in the parameter data block or in the parameter statement, or, if no default value is specified, the member remains undefined.

Since the tabular data record provides two subscripts for each value, either the parameter or the slice currently used must be 2-dimensional.

Transposed tabular data record

The transposed tabular data record has the following syntactic form:

(tr) : c1 c2 ... cn :=
r1 a11 a12 ... a1n
r2 a21 a22 ... a2n
... ... ... ... ...
rm am1 am2 ... amn

(In this case the delimiter : following the keyword (tr) is optional and may be omitted.)

This data record is completely analogous to the tabular data record (see above) with the only exception that the first subscript defined by the element aij is cj while the second one is ri.

Being once specified the (tr) indicator effects on all subsequent data records until either a slice or the end of data block has been encountered.

Tabbing data format

The parameter data block in the tabbing format has the following syntactic form:

     param default value : s :  p1 ,  p2 , ...,  pk :=
     t11 , t12 , ... , t1n ,   a11 , a12 , ..., a1k
     t21 , t22 , ... , t2n ,   a21 , a22 , ..., a2k
       .  .  .  .  .  .  .  .  .  .  .  .  .  .  .
     tm1 , tm2 , ... , tmn ,   am1 , am2 , ..., amk ;
Note:
The keyword default may be omitted along with a value following it.
The symbolic name s of a set may be omitted along with the colon following it.
All comae are optional and may be omitted.

The data block in the tabbing format shown above is exactly equivalent to the following data blocks:

     set s := (t11,...,t1n) (t21,...,t2n) ... (tm1,...,tmn)
     
     param pj default value :=
              [t11,...,t1n] a1j [t21,...,t2n] a2j ... [tm1,...,tmn] amj;

where j = 1, 2, ..., k.


Next: , Previous: Model data, Up: Top

Appendix A Solving models with glpsol

The GLPK package4 includes the program glpsol, which is a stand-alone LP/MIP solver. This program can be invoked from the command line or from the shell to solve models written in the GNU MathProg modeling language.

In order to tell the solver that the input file contains a model description, the option --model should be specified in the command line. For example:

     glpsol --model foobar.mod

Sometimes it is necessary to use the data section placed in another file, in which case the following command may be used:

     glpsol --model foobar.mod --data foobar.dat

Note that if the model file also contains the data section, that section is ignored.

If the model description contains some display and/or print statements, by default the output goes to the terminal. In order to redirect the output to a file the following command may be used:

     glpsol --model foobar.mod --display foobar.out

If you need to look at the problem which has been generated by the model translator, the option --wtxt can be specified in the command line as follows:

     glpsol --model foobar.mod --wtxt foobar.txt

in which case the problem will be written to the file foobar.txt in plain text format suitable for visual analysis.

Sometimes it is necessary merely to check the model description not solving the generated problem. In this case the option --check should be given in the command line, for example:

     glpsol --check --model foobar.mod --wtxt foobar.txt

In order to write a numeric solution obtained by the solver the following command may be used:

     glpsol --model foobar.mod --output foobar.sol

in which case the solution will be written to the file foobar.sol in plain text format.

Complete list of the glpsol options can be found in the reference manual included in the GLPK distribution.


Next: , Previous: Solving models with glpsol, Up: Top

Appendix B Example model description

Model description written in GNU MathProg

Here is a complete example of the model description written in the GNU MathProg modeling language.

# A TRANSPORTATION PROBLEM
#
# This problem finds a least cost shipping schedule that meets
# requirements at markets and supplies at factories.
#
#  References:
#              Dantzig G B, "Linear Programming and Extensions."
#              Princeton University Press, Princeton, New Jersey, 1963,
#              Chapter 3-3.

set I;
/* canning plants */

set J;
/* markets */

param a{i in I};
/* capacity of plant i in cases */

param b{j in J};
/* demand at market j in cases */

param d{i in I, j in J};
/* distance in thousands of miles */

param f;
/* freight in dollars per case per thousand miles */

param c{i in I, j in J} := f * d[i,j] / 1000;
/* transport cost in thousands of dollars per case */

var x{i in I, j in J} >= 0;
/* shipment quantities in cases */

minimize cost: sum{i in I, j in J} c[i,j] * x[i,j];
/* total transportation costs in thousands of dollars */

s.t. supply{i in I}: sum{j in J} x[i,j] <= a[i];
/* observe supply limit at plant i */

s.t. demand{j in J}: sum{i in I} x[i,j] >= b[j];
/* satisfy demand at market j */

data;

set I := Seattle San-Diego;

set J := New-York Chicago Topeka;

param a := Seattle     350
           San-Diego   600;

param b := New-York    325
           Chicago     300
           Topeka      275;

param d :              New-York   Chicago   Topeka :=
           Seattle     2.5        1.7       1.8
           San-Diego   2.5        1.8       1.4  ;

param f := 90;

end;

Generated LP problem

Here is the result of the translation of the example model produced by the solver glpsol and written in the free MPS format.

NAME transp
ROWS
 N cost
 L supply[Seattle]
 L supply[San-Diego]
 G demand[New-York]
 G demand[Chicago]
 G demand[Topeka]
COLUMNS
 x[Seattle,New-York] cost 0.225 supply[Seattle] 1
 x[Seattle,New-York] demand[New-York] 1
 x[Seattle,Chicago] cost 0.153 supply[Seattle] 1
 x[Seattle,Chicago] demand[Chicago] 1
 x[Seattle,Topeka] cost 0.162 supply[Seattle] 1
 x[Seattle,Topeka] demand[Topeka] 1
 x[San-Diego,New-York] cost 0.225 supply[San-Diego] 1
 x[San-Diego,New-York] demand[New-York] 1
 x[San-Diego,Chicago] cost 0.162 supply[San-Diego] 1
 x[San-Diego,Chicago] demand[Chicago] 1
 x[San-Diego,Topeka] cost 0.126 supply[San-Diego] 1
 x[San-Diego,Topeka] demand[Topeka] 1
RHS
 RHS1 supply[Seattle] 350 supply[San-Diego] 600
 RHS1 demand[New-York] 325 demand[Chicago] 300
 RHS1 demand[Topeka] 275
ENDATA

Optimal LP solution

Here is the optimal solution of the generated LP problem found by the solver glpsol and written in plain text format.

     
     Problem:    transp
     Rows:       6
     Columns:    6
     Non-zeros:  18
     Status:     OPTIMAL
     Objective:  cost = 153.675 (MINimum)
     
        No.   Row name   St   Activity     Lower bound   Upper bound    Marginal
     ------ ------------ -- ------------- ------------- ------------- -------------
          1 cost         B        153.675
          2 supply[Seattle]
                         B            300                         350
          3 supply[San-Diego]
                         NU           600                         600         < eps
          4 demand[New-York]
                         NL           325           325                       0.225
          5 demand[Chicago]
                         NL           300           300                       0.153
          6 demand[Topeka]
                         NL           275           275                       0.126
     
        No. Column name  St   Activity     Lower bound   Upper bound    Marginal
     ------ ------------ -- ------------- ------------- ------------- -------------
          1 x[Seattle,New-York]
                         B              0             0               
          2 x[Seattle,Chicago]
                         B            300             0               
          3 x[Seattle,Topeka]
                         NL             0             0                       0.036
          4 x[San-Diego,New-York]
                         B            325             0               
          5 x[San-Diego,Chicago]
                         NL             0             0                       0.009
          6 x[San-Diego,Topeka]
                         B            275             0               
     
     End of output


Previous: Example model description, Up: Top

Acknowledgements

The author would like to thank the following people, who kindly read, commented, and corrected the draft of this manual:

Juan Carlos Borras <borras@cs.helsinki.fi>

Harley Mackenzie <hjm@bigpond.com>

Robbie Morrison <robbie@actrix.co.nz>


Footnotes

[1] The GNU MathProg language is a subset of the AMPL language. Its GLPK implementation is mainly based on the paper: Robert Fourer, David M. Gay, and Brian W. Kernighan, “A Modeling Language for Mathematical Programming.” Management Science 36 (1990) pp. 519-54.

[2] There is another way to specify data for a simple set along with data for parameters. This feature is discussed in the next section.

[3] Data record is simply a technical term. It does not mean that data records have any special formatting.

[4] <http://www.gnu.org/software/glpk/>