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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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