xpress.constraint
Purpose
Class for linear, quadratic, and nonlinear constraints.
Synopsis
c = xpress.constraint (constraint=None, body=None, lb=-xpress.infinity, ub=xpress.infinity, sense=None, rhs=None, name='')
Arguments
|
constraint
|
The constraint, written as a
==,
<=, or
>= condition between two expressions. Variables can appear on either or both sides of the sign. Example: x1 + 2 * x2 <= 4 |
|
body
|
An expression indicating the function to be constrained between
lb and
ub or by
rhs with an assigned
sense. It should not be used when
constraint is defined. Example: 3 * x1 + x2
|
|
lb
|
Lower bound on
body.
|
|
ub
|
Upper bound on
body.
|
|
sense
|
Sign of the constraint: one of
xpress.leq,
xpress.eq,
xpress.geq, or
xpress.range.
|
|
rhs
|
Right-hand side of the constraint if
sense is defined. It may not be specified if
lb or
ub are.
|
|
name
|
Name of the constraint (string).
|
Example
Constraint declared without the explicit constructor:
myconstr = x1 + x2 * (x2 + 1) <= 4
One or more constraints (or vectors of constraints) can be added to a problem via the addConstraint method:
m.addConstraint(myconstr) m.addConstraint(v1 + v2 <= 3) m.addConstraint(x[i] + y[i] <= 2 for i in range (10))
In order to help formulate compact problems, the Sum operator of the xpress module can be used to express sums of expressions. Its argument is a list of expressions (linear or quadratic):
m.addConstraint(xp.Sum ([y[i] for i in range (10)]) <= 1) m.addConstraint(xp.Sum ([x[i]**2 for i in range (9)]) <= x[9])
Further information
1. Parameters lb, ub, and rhs must be constant.
2. A constraint can be specified more naturally as a condition on a linear or quadratic expression:
3. When handling variables or expressions, it is advised to use the Sum operator in the Xpress module rather than the native Python operator, for reasons of efficiency.
Related topics
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