[Cbc] Cbc CLI Infeasible Error

[John Forrest]

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.

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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