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## Re: [Help-glpk] multiplication of linear forms not allowed

**From**: |
Andrew Walbran |

**Subject**: |
Re: [Help-glpk] multiplication of linear forms not allowed |

**Date**: |
Wed, 30 Nov 2005 17:45:29 +1300 |

**User-agent**: |
KMail/1.8.2 |

On Wed, 30 Nov 2005 7:41 am, Jorge Tavares wrote:
>* Dear GLPK users,*
[snip]
>* In the first model, my constraint was:*
>
>* s.t. constraint{i in I}: sum{j in J} (r[i,j] * x[j]) <= c[i];*
>
>* and now it must be:*
>
>* s.t. constraint: sum{j in J} (sum{i in I} (a[i] * r[i,j]) * x[j]) <=*
>* sum{i in I} (a[i] * c[i]);*
>
>* But when I run glpsol, it doesn't accept the following formulation*
>* because of the multiplication of x[j]. It gives the error:*
>* "multiplication of linear forms not allowed".*
Could you please clarify which of a, r, x, c are variables, and which are
parameters?
If a is a parameter, the following might work:
constraint: sum{j in J} (sum{i in I} (a[i] * r[i,j] * x[j])) <= sum{i in I}
(a[i] * c[i]);
If both a and r are variables, then this is not a linear program, and GLPK
cannot solve it (at least not without first rewriting it to be linear, if
possible).
Andrew Walbran