[Coin-discuss] writing out a maximising MPS/LP problem in OsiClpSolver

[Kish Shen]

Hi,

I am unable to write out a maximising problem correctly in LP (with writeLp()) or MPS 
(with writeMps()) format  in OsiClpSolverInterface -- the written file always seems to be 
written out as the minimising problem, e.g. for the problem

Maximize
obj: x0
Subject To
cons0:  x0 - x1 = 0
cons1:  x0 + x1 <= 3
Bounds
 x0 Free
 x1 Free
End

is written as:

Minimize
obj: x0
Subject To
cons0:  x0 - x1 = 0
cons1:  x0 + x1 <= 3
Bounds
 x0 Free
 x1 Free
End

to write this problem, I call writeLp() as follows:

	    lp->Solver->writeLp(file, "", 1e-5, 10, 10, lp->Solver->getObjSense());

where lp->Solver is a OsiClpSolverInterface, and I have checked that lp->Solver->getObjSense()
is -1.0, i.e. maximising.  In fact the same lp file is written if lp->Solver->getObjSense() is 1.0.

In OsiSymSolverInterface, the same call writes out the problem as a minimising problem, but
the sign of the objective is reversed, so it is correct:

Minimize
obj: -x0

Am I calling writeLp (and similarly for writeMps) correctly? 

Thanks in advance for any information and help!

Kish Shen