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Re: [Help-glpk] Parsing large, sparse mathprog model takes a (very) long

From: Meketon, Marc
Subject: Re: [Help-glpk] Parsing large, sparse mathprog model takes a (very) long time
Date: Mon, 2 May 2011 08:17:41 -0500

Beautiful.  I could use this often.

-----Original Message-----
From: Andrew Makhorin [mailto:address@hidden
Sent: Monday, May 02, 2011 9:15 AM
To: Meketon, Marc
Cc: address@hidden
Subject: RE: [Help-glpk] Parsing large, sparse mathprog model takes a (very) 
long time

>  This "data " statement seems very useful.  Could you please provide a
> couple of paragraphs on how the "data" statement works?

The idea is quite simple. Imagine that you declare a plain set:

set S{i,j,k,l,m};

which is provided with data in the data section. However, actually you need to 
have, say, array of sets T{j,m}, where T[j,m] is a set of triplets (l,i,k) from 
S. Using the data attribute (not documented!) you can declare T as follows:

set T{j,m}, data S[2,5,4,1,3];

This declaration has the same effect as there were corresponding data provided 
for T in the data section. [2,5,4,1,3] is a permutation of component indices: 
2nd and 5th components of every 5-tuple in S give pair [j,m] used to index 
elements of T, and 4th, 1st, and 3rd components of the 5-tuple are used to 
build triplets (l,i,k), which are included in set T[j,m].

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