[Cbc] Switch off postsolve?

[Marcel Hunting]

John,

I upgraded CBC to 2.8.0 and with that version the model runs fine.

Thanks a lot!

Marcel


From: cbc-bounces at list.coin-or.org [mailto:cbc-bounces at list.coin-or.org] On Behalf Of John Forrest
Sent: Thursday, April 18, 2013 6:10 PM
To: cbc at list.coin-or.org
Subject: Re: [Cbc] Switch off postsolve?

Marcel,

I can get a similar error using 2.7.5.  I have also tried 2.7.8 and that was fine.  I would suggest upgrading to at least 2.7.8.

John Forrest
On 18/04/13 11:53, Marcel Hunting wrote:
Hi,

I have a small MIP problem for which CBC 2.7.5 returns infeasible while the problem is in fact feasible. This is part of the log file:

Optimal - objective value 5625.1701
Integer solution of -5625.1701 found by feasibility pump after 0 iterations and 0 nodes (0.17 seconds)
Objective coefficients multiple of 0.1
Search completed - best objective -5625.170085470087, took 0 iterations and 0 nodes (0.18 seconds)
Maximum depth 0, 0 variables fixed on reduced cost
0  Obj 5625.1701 Primal inf 2.2580657 (48)
3  Obj 5623.2228 Primal inf 5.4953389 (94)
...
40  Obj 5612.1607 Primal inf 1.3658683 (28)
Primal infeasible - objective value 5612.1607

The objective value (5625.1701) of the integer solution found by the feasibility pump algorithm corresponds to the objective value of the optimal solution.

It seems that CBC does some kind of postsolve which fixes variables and that appears to be infeasible. Does CBC have a parameter to switch off the postsolve?

I can provide a LP or MPS file of the model. The scaling of the model seems ok.

Best regards,

Marcel Hunting




_______________________________________________

Cbc mailing list

Cbc at list.coin-or.org<mailto:Cbc at list.coin-or.org>

http://list.coin-or.org/mailman/listinfo/cbc

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://list.coin-or.org/pipermail/cbc/attachments/20130419/fb6f0e19/attachment.html>