Loop#

class gamspy.Loop(indices: Set | Alias | ImplicitSet | Condition | Domain | Sequence[Set | Alias])[source]#

Bases: object

A context manager to execute a group of statements iteratively for each member of a set or domain.

The Loop class maps to the GAMS loop statement. It is particularly useful for cases where parallel assignments are not sufficient, such as iterative calculations, nested loops, or modifying models and solving them repeatedly.

Parameters:
indicesSet | Alias | ImplicitSet | Condition | Domain | Sequence[Set | Alias]

The controlling domain of the loop. This can be a single Set, a sequence of Sets, or a domain restricted by a logical condition (using .where).

Examples

1. Simple iteration over a single Set:

>>> import gamspy as gp
>>> m = gp.Container()
>>> t = gp.Set(m, records=["1985", "1986", "1987"])
>>> pop = gp.Parameter(m, domain=t, records=[("1985", 3456)])
>>> growth = gp.Parameter(m, domain=t, records=[("1985", 25.3), ("1986", 27.3)])
>>> with gp.Loop(t):
...     pop[t + 1] = pop[t] + growth[t]

2. Iteration with a logical condition (dollar condition): You can restrict the loop domain using the .where attribute on Sets or Domains.

>>> i = gp.Set(m, records=["i1", "i2", "i3"])
>>> j = gp.Set(m, records=["j1", "j2", "j3"])
>>> q = gp.Parameter(m, domain=[i, j], records=[("i1", "j1", 1), ("i1", "j2", 3)])
>>> x = gp.Parameter(m, records=1)
>>> with gp.Loop(gp.Domain(i, j).where[q[i, j] > 0]):
...     x[...] = x[...] + q[i, j]

3. Nested Loops: Loops can be nested using standard Python indentation.

>>> a = gp.Parameter(m, domain=[i, j])
>>> b = gp.Parameter(m)
>>> a.generateRecords()
>>> with gp.Loop(i):
...     with gp.Loop(j):
...         b[...] = a[i, j]
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