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Re: [Help-glpk] Calculate sqrt of var

From: Andrew Makhorin
Subject: Re: [Help-glpk] Calculate sqrt of var
Date: Tue, 08 Apr 2014 23:34:27 +0400

On Tue, 2014-04-08 at 18:46 +0100, Tiago Costa wrote:
> Hi,
> I'm trying to apply the following restriction:
> subject to calc2 {m in M} :
>      fee[m] = sqrt(1000 + (100 + (sum {n in N} (n mod 47))) * (sum {l in 
> L} prod[l,m]));
> However since prod[l,m] is a var, I get "argument for sqrt has invalid 
> type".
> I've read in the documentation that you can only calculate the sqrt of 
> constants/params/etc so is there a workaround to calculate the sqrt of a 
> var?
> Thanks
> --
> Tiago Costa

Only linear constraints are allowed while sqrt makes the constraint
non-linear. However, using sqrt *below* the solve statement, i.e. when
all the variables have been computed, is allowed.

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