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## Re: [Help-glpk] is there a function for count in MATHPROG?

**From**: |
Andrew Makhorin |

**Subject**: |
Re: [Help-glpk] is there a function for count in MATHPROG? |

**Date**: |
Sat, 07 Apr 2012 01:36:01 +0400 |

>* I'm looking for a function that count number of objects that belong to a *
>* specific cluster but I dont know if such function exists.*
>* *
>* For example I'm trying to count number of objects in variable Z[i] but *
>* with Cardinal function I get an error tha says "invalid preceding *
>* operator == " what does it mean?*
>* s.t. Proporcion{k in 1..card(CATEGORIAS)}: card({i in ITEMS: k in *
>* Z[i]}) <= noitems*Porcentaje[k];*
You cannot write 'k in Z[i]', because Z[i] is not a set.
Assuming that Z models an indicator function (does it?) of a subset of
some predefined set, which (subset) needs to be found, and Z[i] is a
binary variable, the cardinality of that subset can be expressed as
'sum{i in ...} Z[i]', so you could write your constraint as follows:
s.t. Proporcion{k in 1..card(CATEGORIAS)}:
sum{i in ITEMS: k in ...} noitems * Porcentaje[k] * Z[i];