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Re: [Help-glpk] Solving a large LP problem

From: Samik Raychaudhuri
Subject: Re: [Help-glpk] Solving a large LP problem
Date: Thu, 15 Jul 2004 12:10:05 -0400
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7) Gecko/20040514

Thanks Andrew, I will try submitting the problem to NEOS solver.
I had one question though. My output seems to be showing that the presolve stage is already over and its trying to solve the presolved problem. In that case, will --nopresol be of any use?
I will try to find out the system settings as mentioned by you.

On 7/15/2004 12:05 PM, Andrew Makhorin wrote:

This is the output I got when I solved with a considerably smaller problem.
$ glpsol --mps new.mps
load_mps: reading LP data from `new.mps'...
load_mps: name `BLANK'
load_mps: 243742 rows
load_mps: 364514 columns
load_mps: 1148311 non-zeros
load_mps: 1 right-hand side vector(s)
load_mps: 0 range vector(s)
load_mps: 0 bound vector(s)
load_mps: 932145 cards were read
lpx_simplex: original LP has 243742 rows, 364514 columns, 1148311 non-zeros
lpx_simplex: presolved LP has 90344 rows, 203072 columns, 487180 non-zeros
lpx_adv_basis: size of triangular part = 89732
umalloc: size = 3614184; malloc failed
Is this b/c I have less system memory available, or b/c of something to do with the code? How can I check if system memory is the problem.

The last message means that some glpk routine attempted to allocate a
memory block of 3,614,184 bytes long, however, the control program
could not satisfy the request (i.e. malloc returned NULL). As a rule
this happens if the machine has not enough ram memory. You can try to
specify the option `--nopresol', because presolver data structures
eat up much ram memory (although for your instance using the presolver
has a significant effect). The error also may happen due to some system
settings which limit the amount of ram memory allocated to application

Btw, glpsol 4.4 is installed on the NEOS Server:
You can try to submit your mps file to the server at least to see
whether glpsol is able to solve your instance.

Andrew Makhorin

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