[Coin-discuss] OsiClp: problem with sign of objective value
John J Forrest
jjforre at us.ibm.com
Sat Aug 12 04:50:39 EDT 2006
should be fixed now
Kish Shen
<kish.shen at crossc
oreop.com> To
Sent by: coin-discuss at list.coin-or.org
coin-discuss-boun cc
ces at list.coin-or.
org Subject
Re: [Coin-discuss] OsiClp: problem
with sign of objective value
08/11/06 12:22 AM
Please respond to
Discussions about
open source
software for
Operations
Research
<coin-discuss at lis
t.coin-or.org>
Hi,
I have done some more tests on this problem. For the problem (in LP
format):
Maximize
obj: x0
Subject To
Bounds
0 <= x0 <= 1
End
when I try to solve the above problem (produced by calling
OsiSolverInterface functions, rather
than from reading in the LP or MPS file) in ClpSolverInterface. The
objective value is
incorrectly returned as -1 rather than 1. If I add a dummy constraint,
e.g.
Maximize
obj: x0
Subject To
cons0: x0 >= -100000000000000000000
Bounds
0 <= x0 <= 1
End
the objective value is then correctly returned as 1.
I have tried to trace the execution of both problems, and the objective
value in the ClpModel,
stored in objectiveValue_, is different in the above two cases. It is 1 in
the first case (without
the dummy constraint) and -1 in the second (with the dummy constraint. This
objective value is
then multiplied by the objective sense (-1 for maximising) and this gives
the -1 and 1 objective
value respectively.
I tried to trace the execution further to see why there is this difference,
but I was not really
able to follow what Clp was doing.
Any suggestions of how I can work round this problem, so that I can get the
correct objective
value in the first case? Thanks in advance for any help!
Kish Shen
_______________________________________________
Coin-discuss mailing list
Coin-discuss at list.coin-or.org
http://list.coin-or.org/mailman/listinfo/coin-discuss
More information about the Coin-discuss
mailing list