[Coin-discuss] Cplex use termination code "abandoned" if presolve determines that problem is infeasible or unbounded.

[Laszlo Ladanyi]

Hi Tommy,

The FIXME refers to the question of what is the proper course of action in
case the LP solver has abandoned the problem (numerical difficulties, etc.).
Right now BCP just throws an exception, but perhaps it would be better to
prune the node and get the opt for the rest.

The real problem lies in OsiCpxSolverInterface. Apparently when the cplex
presolver finishes off the problem the interface does not deduce correctly the
status (abandoned, optimal, primal/dual infeas/unbounded, etc.) and comes back
with abandoned instead of infeasible. Hopefully the maintainer will fix it
soon, I can look at it next week if noone fixes it earlier. If you'd like to
wet your feet then look at COIN/Osi/OsiCpx/OsiCpxSolverInterface.cpp and look
at the functions below the comment:
// Methods returning info on how the solution process terminated

Good luck,
--Laci

On Tue, 13 May 2003, Tommy Thomadsen wrote:

> Hi,
> 
> I have a problem using BCP with CPLEX - I get a fatal error resulting
> from the following lines in BCP_lp_main_loop.cpp:
> if (tc & BCP_Abandoned) {
>    // *FIXME* : later we might want to prune this node, but continue
>    throw BCP_fatal_error("LP solver abandoned the lp.\n");
> }
> 
> Info from Cplex:
> CPLEX Error  1101: Presolve determines problem is infeasible or unbounded.
> CPLEX Error  1217: No solution exists.
> 
> This does not happen when using CLP.
> 
> As the "FIXME" suggests, the node should be pruned since it is infeasible
> (agreed?), but I have no idea how to accomplish that.
> 
> Any help will be appreciated very much!
> 
> Regards,
> Tommy
> 
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