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[Help-glpk] solve, add rows, resolve

From: Brady Hunsaker
Subject: [Help-glpk] solve, add rows, resolve
Date: Mon, 15 May 2006 12:33:32 -0400
User-agent: Thunderbird (X11/20060501)


I had previously thought that it was possible to do the following:

- create an LP instance
- solve with lpx_simplex()
- add rows with lpx_add_rows() and related functions
- re-solve starting from the same basis with lpx_simplex() with LPX_K_DUAL set

However, this doesn't work for me. This issue arose in testing the COIN-OR OSI interface, which expects that this is possible.

In fact, lpx_simplex may even abort without solving on the second attempt (it realizes that it's not a "fresh" problem, but the basis isn't there, or something like that).

Here are my questions:

- What behavior do you currently expect if rows are added and then lpx_simplex is solved? (Solve again from existing basis, solve again as if it were a new instance, something else)

- Would you be interested in a patch that allows re-solving from the existing basis if possible? (I might be able to write such a patch.)

- Do you want me to create a small test case to demonstrate the issue?


Brady Hunsaker
Assistant Professor
Industrial Engineering
University of Pittsburgh

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