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## Re: [Help-glpk] Questions to MathProg

**From**: |
Andrew Makhorin |

**Subject**: |
Re: [Help-glpk] Questions to MathProg |

**Date**: |
Thu, 12 May 2005 03:11:30 +0400 |

>*> 2) I have a restriction of the form*
>*> s.t. Rb{v1 in V,v2 in V: v1<v2}: ...*
>*> This works, if V contains numbers. If V contains symbols, v1<v2 is not*
>*> allowed.*
>*> Is there a function to convert symbols to their position in the set or*
>*> something like that?*
>* *
>* Yes, this is explained in the discussion of "ordered sets" in Section 5.6 of*
>* the AMPL book. If you don't have the book, you may be able to figure out*
>* what you need by looking at the following example:*
>* *
>* www.ampl.com/BOOK/EXAMPLES/steelT2.mod*
>* www.ampl.com/BOOK/EXAMPLES/steelT2.dat*
Unfortunately "ordered sets" are not implemented in MathProg.
(The reason was that the AMPL implementation seems to be very
artificial. Introducing a binary relation between set's elements could
be more natural way, however, this feature is incompatible with AMPL.)
Andrew Makhorin