[Symphony] LP solver (Clp) won't stop after TM_time_limit & 2 newbie questions

[Ashutosh Mahajan]

hi Pierre

On Tue, 09 Sep 2008, lebodicp at insa-rouen.fr wrote:

> Hello,
> 
> I have implemented an integer linear program thanks to the SYMPHONY user
> callback functions. Few of them are redefined for now. I'm using the
> symphony environment rather than the osi. I'm using an embedded parser
> that reads custom data files rather than mps files. I'm handling large
> problems (possibly 150000 variables and 100000 constraints). Finally, I
> use Clp.
> The program by itself works as expected: small problems are solved, large
> problems are rarely solved.
> I have encountered a few problems during further usage. I'm new to
> SYMPHONY, so those probably aren't bugs.
> 
> -From the source code, setting TM_time_limit in the parameter file should
> set LP time limit to the same value. As I'm handling large problems, it is
> often the case when lp solving at root node is itself too long. However,
> the LP solver never seems to stop after the time limit, or stops way after
> it (way!). TM_time_limit affects TM behavior as expected though. Is this a
> desired behavior? Am I doing something wrong? Is this a bug?

we dont pass time limit to LP solver yet. so yes, it is a limitation as of
now. we will try to fix this soon.

> 
> -I've tried using column generation, but couldn't get it right (for my
> problem, variables are known from the start as required in SYMPHONY). I
> followed the manual instructions but obviously I'm doing something wrong.
> I can't find an example that uses column generation. Is there something of
> that kind available?

column generation hasnt been tested in a while. so i am not sure if its a
problem in symphony or with how you call it. more information about where it
seems broken may help. is it not compiling? or crashing? or giving unexpected
output?

> 
> -I didn't realize using sym environment rather than osi would prevent me
> from using Cgl cuts. Now that the code is written, what would be the
> easiest way to get Cgl cuts to work? Would it be possible to (1)export to
> mps (2)read the mps file with another program that uses osi? What would be
> the best way?

This behaviour is unexpected.  what version of symphony are you using and on
which platform? you can increase the verbosity level by using '-v 10' and see if
cuts are actually generated. did you also modify user_generate_cuts_in_lp()
function? if so, can you post it as well?

> Thanks.
> 
> Best, Pierre
> 
> 
> 
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--
regards
Ashutosh Mahajan
http://coral.ie.lehigh.edu/~asm4