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From: | Meketon, Marc |
Subject: | Re: [Help-glpk] Condensing a sparse matrix by creating a subset of parameter data |
Date: | Thu, 31 Mar 2016 09:10:57 -0500 |
Are you looking for something like the below that finds the subset of nodes being used? set nodes := {"A", "B", "C", "D", "E"}; set arcs within nodes cross nodes := {("A","B"), ("B","E")}; display nodes; display arcs; set nodes_that_are_used :=
setof{tail_node in nodes, head_node in nodes : (tail_node, head_node) in arcs } tail_node union setof{tail_node in nodes, head_node in nodes : (tail_node, head_node) in arcs } head_node;
display nodes_that_are_used; end; From: help-glpk-bounces+address@hidden [mailto:help-glpk-bounces+address@hidden
On Behalf Of Abhishek Shivakumar Hi, I have an lp model that produces an extremely sparse constraint matrix. I would like to reduce the number of non-zero entries in this matrix (make the matrix more dense). The main cause of this sparse-ness is the relation between two parameters.
They can be seen as ‘arcs’ and ‘nodes: not all nodes have arcs between them. Is there a way to create a subset of parameter data from the sets ‘arcs’ and ‘nodes’ based on whether they are connected? I would then be able to apply constraints only for this subset.
In other languages (such as python) such an operation is possible through nested conditional statements. Is there a similar/equivalent approach in glpk/GNU mathprog? Thanks! Abhishek This e-mail and any attachments may be confidential or legally privileged. If you received this message in error or are not the intended recipient, you should destroy the e-mail message and any attachments or copies, and you are prohibited from retaining, distributing, disclosing or using any information contained herein. Please inform us of the erroneous delivery by return e-mail. Thank you for your cooperation. |
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