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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 13:02:51 +0400 |

>* i am searching for an expression equal to the mathematicl sign function.*
>* I have a sum in a "subject to" statement, and i want the returning value of*
>* this sum to be zero if the sum is 0 or to be one if the sum is greater than*
>* 0.*
>* Example:*
>* subject to rooms{a in A}: sum{b in B} sign(sum{c in C} x[a,b,c]) <= r;*
>* whereas x is a variable only containing binary values.*
>* any ideas?*
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;