Re: [Help-glpk] [Fwd: GLPK Mathprog model]

[Xypron]

Hello Alan,

please, register for the help list to have your mail directly received, see
http://lists.gnu.org/mailman/listinfo/help-glpk

> var f{k in 1..K} = sum{i in 1..I, j in 1..J} x[i,j,k]*w[i] ;

In AMPL this is called a defined variable. The statement does not 
declare a structural variable but works like kind of a macro. Each 
occurance of f[k] will be replaced by sum{i in 1..I, j in 1..J} 
x[i,j,k]*w[i] (see Robert Fourer, David M.Gay, Brian W. Kerninghan, 
"AMPL - A modeling Language for Mathematical Programming", 2nd ed, p. 131).

This is not possible in GMPL.

You could use a structural variable

var f{k in 1..K};

and a constraint

s.t. c1{k in 1..K} :
  f[k] = sum{i in 1..I, j in 1..J} x[i,j,k]*w[i];

But this may render your problem harder to solve.

Best regards

Xypron


> -------- Forwarded Message --------
> From: Alan Zinober<address@hidden>
> To: address@hidden
> Subject: GLPK Mathprog model
> Date: Thu, 27 Jan 2011 09:27:21 +0000
>
>
> The model below (only relevant parts included) is taken from a working
> AMPL model program
> that is solved running in AMPL.
>
> I am trying to run the same problem using GLPK (Mathprog) but there is
> an error reported on the last line below.
>
> According to the guidance manual the text below seems fine. Any advice
> will be most welcome.
>
> GLPK "report":
>
> Reading model section from G-case7-a26Suli.txt...
> G-case7-a26Suli.txt:47: expression following = has invalid type
> Context: ...um { i in 1 .. I , j in 1 .. J } x [ i , j , k ] * w [ i ] ;
> MathProg model processing error
>
>      Alan
>
> #---------------------------------------PARAMETERS
> param I;
> param J;
> param K;
>
> param w{1..I};             # wt per type i pack
>
> #---------------------------------------VARIABLES
>
> var x{1..I, 1..J, 1..K}, binary;
>
> var f{k in 1..K} = sum{i in 1..I, j in 1..J}  x[i,j,k]*w[i] ;
>
>
>
>
>
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