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## Re: [Help-glpk] Sign of an integer

**From**: |
Andrew Makhorin |

**Subject**: |
Re: [Help-glpk] Sign of an integer |

**Date**: |
Mon, 7 Apr 2008 13:10:47 +0400 |

>* var sx{a in A, b in B}, binary;*
>* /* sx[a,b] is sign(sum{c in C} x[a,b,c]) */*
>* /* in other word, sx[a,b] is logical_or{c in C} x[a,b,c] */*
>* *
>* s.t. foo{a in A, b in B}: sum{c in C} x[a,b,c] <= card(C) * sx[a,b];*
>* *
>* s.t. rooms{a in A}: sum{b in B} sx[a,b] <= r;*
Incorrect. The first constraint must be the following:
s.t. foo{a in A, b in B}:
0 <= card(C) * sx[a,b] - sum{c in C} x[a,b,c] <= card(C) - 1;