[Clp] Objective is nan (sometimes assertion failure)

[Aleksandr M. Kazachkov]

The objective is all-zeroes, because I was just checking feasibility at the
point the error occurred. When presolve is on, it solves to optimality
(objective value 0) and says that it is feasible. When presolve is off, I
get nan or an assertion failure.

Now, if I add the first >= constraint as the objective (it is a
minimization problem), we should be either primal infeasible or optimal.
When presolve is on, I get optimal; when presolve is off, I get "Clp0001I
Primal infeasible - objective value -nan".

The lp file with the new objective is attached.

On Sat, May 6, 2017 at 6:32 PM Sébastien Roy <sebastien.roy.sr at gmail.com>
wrote:

> This usually means your linear program is unbounded so the objective
> function value is infinity. If your modeling a problem that should bound
> you must have an error in your linear program model.
>
> On Sat, May 6, 2017 at 6:20 PM, Aleksandr M. Kazachkov <akazachk at cmu.edu>
> wrote:
>
>> Hi everyone,
>>
>> I am not sure if there is something wrong with my setup, or if this is a
>> bug, but I would appreciate any help in either case. Thank you in advance!
>>
>> I have Clp version 1.16 set up on a Fedora machine. The compilation
>> options are: enable_debug=yes, enable_gnu_packages=yes, and I am using blas
>> and lapack. There are no problems when I run "make test".
>>
>> However, on the following LP (which solves fine when using Bcp-1.4.3,
>> which maybe is using an older version of Clp), when presolve (initial) is
>> off, I get that the objective value is "nan". In the context this LP came
>> up (but not when I saved it and ran it on its own), I got the following
>> assertion failure:
>> ../../../Clp/src/ClpSimplexDual.cpp:3216: int
>> ClpSimplexDual::changeBounds(int, CoinIndexedVector*, double&): Assertion
>> `!("should not be here")' failed.
>>
>> Specifically, I get the error after the following two lines:
>>   solver.setHintParam(OsiDoPresolveInInitial, false);
>>   solver.initialSolve();
>>
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>
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