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Re: [Help-glpk] Calculate sqrt of var

From: Meketon, Marc
Subject: Re: [Help-glpk] Calculate sqrt of var
Date: Tue, 8 Apr 2014 19:11:44 -0500

My guess is that fee[m] is a const/param, so can you rewrite your constraint to 
be the following?

fee[m]*fee[m] = 1000 + (100 + (sum {n in N} (n mod 47))) * (sum {l > in L} 

-----Original Message-----
From: address@hidden [mailto:address@hidden On Behalf Of Andrew Makhorin
Sent: Tuesday, April 08, 2014 3:34 PM
To: Tiago Costa
Cc: address@hidden
Subject: Re: [Help-glpk] Calculate sqrt of var

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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