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Re: [Help-glpk] Some suggestions to GLPK/L

From: Andrew Makhorin
Subject: Re: [Help-glpk] Some suggestions to GLPK/L
Date: Thu, 25 Jul 2002 00:33:03 +0400

>1. numerical set, like mentioned in a previous email.
>It would be convienient if we can simply declare 
>         set S = (1..10000);
>How inconvienient if I have to explictly list 10000
>items in the set.

I agree :+) However all items (i.e. elements of a set) should have
unique names, so integers can't be used (otherwise from the context
'a[#123]' it is unclear which set the item '123' belongs to). The main
issue is the syntax. The context 'set S = (ABC1..ABC1000)' is more or
less clear. But what about 'set S = (ABC1D..ABC1000D)'? May be better to
write something like 'set S = (address@hidden@D, i=1..1000)' ?

>2. import data from external sources. Text files would
>suffice, though it would be better to use with
>database or spreadsheet. Maybe one file for each

Have you got any thoughts about syntax?

>3. some simple functions would be really convienient.
>For example, if I want to find out the maximum value
>in a parameter.

Yes, must add some aggregate functions like sum, i.e. min, max, and
also the quantors 'forall' and 'exist'.

>4. set operations, like union and intersection. 

In glpk/l the same item can't belong to different sets, so these
operations can't be implemented. Nevertheless you can simulate subsets
using predicates. To do that you can declare universum, i.e. a set,
which includes all items, and then define unary predicates, which
determine subsets. Then, say, intersection of sets can be expressed as
conjunction of the corresponding predicates.

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