[Cbc] Cbc CLI Infeasible Error

[Matthew Gidden]

On Wed, Jul 30, 2014 at 12:34 PM, John Forrest <john.forrest at fastercoin.com>
wrote:

>  Matthew,
>
>
> Fixed in trunk - do you want it fixed in stable?
>
Yes, please, if it's not too much trouble =).

>
> OsiPresolve did dual tests before tightening bounds.  As z has positive
> cost and useless coefficient dual tests said put it to lower bound i.e.
> 0.4. Tightening then said integer variable is fixed to 0.4 so infeasible.
> I said it was a stupid bug.
>
Stupid and subtle; I'm glad I could help! It might be reasonable to add it
as a Cbc unit test if you feel so inclined.

Cheers,
Matt

>
> Just moved tightening before dual tests.
>
> John
>
> On 30/07/14 18:17, Matthew Gidden wrote:
>
> Hi John,
>
>
> On Wed, Jul 30, 2014 at 12:11 PM, John Forrest <
> john.forrest at fastercoin.com> wrote:
>
>>  Matthew,
>>
>> Should be easy to fix - looks like a really stupid bug.
>>
>> If I change the lower bounds on y,z to 2,1 it works!  As rounding up
>> should be first thing that happens, you can see why I say stupid.
>>
> Ok, thanks John! I can change my bounds on my unit test for now, but I'm
> glad I was able to bring this to your attention. Thanks again for looking
> into it.
>
>>
>> John Forrest
>>
>>
>> On 30/07/14 16:20, Matthew Gidden wrote:
>>
>>  Hi all,
>>
>>  I've been posting a lot recently.. first of all, thank you for replying!
>>
>>  I've unit tested my application pretty vigorously, and a Cbc API unit
>> test broke when I moved to the CLI implementation. Specifically, I set up
>> the following toy problem:
>>
>>  min 2x + 0.5y + 1.8z
>> st     x  +     y            > 4.4
>>                    y +     z  < 3.1
>> x in [1.3, 5], y in [1.7, 5], z in [0.4, 5]
>> y, z integer
>>
>>  The unit test originally passed using the OsiCbcSolverInterface's
>> initial solve and branch and bound methods. I updated it to use an
>> OsiClpSolverInterface that is fed a CbcModel and call CbcMain0/1 on said
>> model. The unit test now fails with the following relevant output:
>>
>>> Welcome to the CBC MILP Solver
>>> Version: 2.8.7
>>> Build Date: Dec 28 2013
>>> command line - exchng -solve -quit (default strategy 1)
>>> Continuous objective value is 5.47 - 0.00 seconds
>>> Cgl0000I Cut generators found to be infeasible! (or unbounded)
>>> Pre-processing says infeasible or unbounded
>>
>>
>>  To double check that indeed a feasible solution existed, I solved the
>> maximization form of the same instance. Attached are MPS files for the max
>> and min forms, and I have verified the same behavior using the cbc CLI
>> (i.e., min is returned as infeasible and max solves).
>>
>>  I'm curious if anyone can replicate this and/or has any advice.
>>
>>  Cheers,
>>
>>  --
>> Matthew Gidden
>> Ph.D. Candidate, Nuclear Engineering
>> The University of Wisconsin -- Madison
>> Ph. 225.892.3192
>>
>>
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>>
>>
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>
>
>  --
> Matthew Gidden
> Ph.D. Candidate, Nuclear Engineering
> The University of Wisconsin -- Madison
> Ph. 225.892.3192
>
>
>


-- 
Matthew Gidden
Ph.D. Candidate, Nuclear Engineering
The University of Wisconsin -- Madison
Ph. 225.892.3192
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