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[Help-glpk] Are trivial constraint equations an issue?

From: Robbie Morrison
Subject: [Help-glpk] Are trivial constraint equations an issue?
Date: Mon, 07 May 2007 19:28:59 +0200
User-agent: Thunderbird (X11/20070306)

Hello all

Earlier Andrew Makhorin wrote (in relation to a Sudoku
problem) (Message-ID: <address@hidden>):

> Try using the option '--intopt' to enable the
> mip presolver. It may reduce the problem size by
> removing redundant rows and columns.

I am working on a relatively literal energy system
simulation.  Part of the model involves
interconnected units transacting electricity,
natural gas, district heat, and so on.  Ultimately
a (directed acyclic) patchwork of classical
network flow problems needs to be solved --
together with a refinement to avoid low duty (less
than say 50%) usage which thereby introduces binary
variables to cover the shut-down status.

The simulation generates a suitable GLPK problem
using the GLPK C-language APIs.

It would make my C++ coding easier if I could
populate this model with a lot of trivial constraint
equations which simply match the flows between units.
For instance:

  flow-from-generator = flow-to-transmission-line

Is this sensible or would I be better advised to
be resolve these variables before building the
GLPK problem?

Or will the following setting (GLPK 4.11 API)
reduce the problem automatically:

  lpx_set_int_parm(my_lpx, LPX_K_PRESOL, 1);

And will I need to introduce some special
variables to cover gas supply from Russia?  :-)

many thanks in advance

ps: the compile-time (and to a lesser extent the
run-time) version information will also be useful
for this project, hence looking forward to using
4.16, thanks!

Robbie Morrison
PhD student -- policy-oriented energy system simulation
Institute for Energy Engineering (IET)
Technical University of Berlin (TU-Berlin), Germany
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