[Cbc] Unbounded MIP problem returned as infeasible by CBCSolver

[John Forrest]

Kish,

   (model->isProvenInfeasible()) returning true is a bug - the fix is 
modifying code in that function to

  if (!status_ && (bestObjective_ >= 1.0e30  && !secondaryStatus_))

However when I try model->isContinuousUnbounded() it returns true

If I have

printf("status %d secondary %d infeasible %s unbounded %s\n",
  model.status(),model.secondaryStatus(),model.isProvenInfeasible()
      ? "true" : "false",model.isContinuousUnbounded() ? "true" : "false");

in my code I get

status 0 secondary 7 infeasible false unbounded true

with above fix and

status 0 secondary 7 infeasible true unbounded true

without fix.

Can you check isContinuousUnbounded() and if it fails send me some code 
to reproduce?

John Forrest


On 06/03/14 01:17, Kish Shen wrote:
> Hi,
>
> For the following (very simple) problem:
>
> Minimize
> obj: x0
> Subject To
> cons0:  x0 + x1 <= 3
> cons1:  X0 = X1  = 0
> Bounds
>  x0 Free
>  x1 Free
> Integers
> x0
> End
>
> which is unbounded, but when we use CBCSolver to solve this problem, 
> we get the result that the problem is infeasible, specifically,
>
> CbcModel* model;
> .....
> model->isProvenInfeasible() returns 1 (true)
>
> Here is the relevant code we use to determine the status of a problem 
> after calling CbcSolver (via CbcMain0 and CbcMain1) to solve the problem:
>
>
> if (model->isInitialSolveProvenOptimal()) {
>    if (model->isProvenInfeasible()) {
>        ....
>
> For the above problem, the above if .. succeeds, which I think should 
> only be the case if the problem is proven infeasible at the root node, 
> but the root node solve should be unbounded (and in fact if I solve 
> the linear problem with CLP, the result is indeed unbounded), but the 
> test
>
> We actually have code to test if the root node solve is unbounded (in 
> which case we classify the solve result as "Unknown", i.e. either 
> infeasible or unbounded, which was the result I expected for the above 
> problem), but
>
> model->isContinuousUnbounded() returns 0 for the above problem, rather 
> than 1 as I expected.
>
> Is there something I am doing wrong, or is there a problem?
>
> I am using Cbc 2.8, which was downloaded last month (14 Feb).
>
> Thanks in advance for any help.
>
> Cheers,
>
> Kish
>
>
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