Thanks for your message. That is indeed (almost) what I'm looking for. I would like to then apply a constraint to the subset of nodes that are being used. Specifically, I want to set a constraint on the 'flow' between the nodes.
I agree that reducing the matrix size won't have a significant effect on the optimization time. However, we're generating an lp file from our model and the time to generate the lp file is likely to be reduced significantly. I expect that there will be an optimal point between reducing the size of the matrix (and time to generate it) and the optimization time. From: Meketon, Marc [mailto:[email protected]] Sent: 31 March, 2016 4:11 PM To: Abhishek Shivakumar <[email protected]>; [email protected] Subject: RE: [Help-glpk] Condensing a sparse matrix by creating a subset of parameter data 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: [email protected]<mailto:[email protected]> [mailto:[email protected]] On Behalf Of Abhishek Shivakumar Sent: Thursday, March 31, 2016 9:18 AM To: [email protected]<mailto:[email protected]> Subject: [Help-glpk] Condensing a sparse matrix by creating a subset of parameter data 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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