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## Re: [Bug-glpk] 0-ary slice not allowed

**From**: |
Andrew Makhorin |

**Subject**: |
Re: [Bug-glpk] 0-ary slice not allowed |

**Date**: |
Wed, 26 Nov 2008 23:51:12 +0300 |

>*> constraint*
>* *
>*> s.t. cost {i in N, j in N} :*
>*> t[i] - t[j] - sum{(i,j) in E} c[i,j] * x[i,j] >= 0;*
>* *
>*> leads to error*
>* *
>*> 0-ary slice not allowed*
>* *
>*> in glpmpl01.c, function expression_list.*
>* *
>*> My expectation was that the sum is 0 if (i,j) is not an element of E and*
>*> c[i,j] x[i,j] otherwise. This would be in conformance with the usual use*
>*> of domain parameters.*
>* *
>* No, I do not think so. In the strong mathematical sense a composite*
>* index must have at least one free dummy variable; otherwise corresponding*
>* aggregate operator like sum has no meaning. Besides, AMPL also does not*
>* allow that.*
Just for clarity.
Do you agree that the following notation is meaningless?
sum{(2,3) in E} c[i,j] * x[i,j]
This is exactly the same as your example: the composite index has no free
dummy variables.