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

**From**: |
Andrew Makhorin |

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

**Date**: |
Sun, 19 Jun 2011 20:11:28 +0400 |

>* How do we solve Integer Linear Programming formulations of the*
>* Travelling Salesman Problem as in this URL*
>* http://support.sas.com/documentation/cdl/en/ormpug/63352/HTML/default/viewer.htm#ormpug_milpsolver_sect020.htm*
>* *
>* where there is a multiplication operator in the Objective function.*
>* *
>* glpsol complains " multiplication of linear forms not allowed".*
>* *
>* Is there an easy fix to this?*
>* *
>* There are a whole lot of decision problems where we either need to*
>* pick something or leave something, almost always represented by a*
>* boolean integer multiplied with its actual quantitative value.*
>* *
Check that in your model objective coefficients are parameters, not
variables.
You also may look at a similar example model tsp.mod included in the
glpk distribution (see subdirectory examples).