[Coin-symphony] jssp.mod in glpk distribution

[Kendall Bailey]

I'm working on an AMPL driver for the OSI interface, including the
OsiSymSolverInterface.  I've used AMPL v9.1.2 to generate a binary
problem file from the jssp.mod that's included with GLPK.  It's a job
shop scheduling problem.  I can solve it with CPLEX,
OsiCbcSolverInterface and OsiGlpkSolverInterface.  Each returns a
slightly different solution, but all three find the optimal objective
value to be 55.  When I try OsiSymSolverInterface, it claims to find a
proven optimal solution, but the objective is 69.

Since I've just substituted Sym in for Cbc or Glpk and found such
different results, I thought I ask if there's known gotcha's for using
OsiSymSolverInterface that might explain it.  Below is the code to do
the solve, once the constraint matrix, objective and bounds are
retrieved from the AMPL file.  Thanks for any help!

(by the way, solve times were: cplex - 0.5sec, glpk - 1.5min, cbc - 1hour)

I can supply the jssp.mod and/or jssp.nl.

Thanks,
Kendall


   solver->loadProblem(*matrix,LUv,Uvx,objective,LUrhs,Urhsx);

   for( int i = 0; i < numIntegerVars; ++i )
   {
      // continuous vars come first, followed by binary and then
      // other integer vars.
      solver->setInteger( numContinuousVars + i );
   }

   solver->initialSolve();
   if( numIntegerVars )
   {
      // solve for integer vars if there are any
      solver->branchAndBound();
   }