[Osi] OsiClp branchandbound

John J Forrest jjforre at us.ibm.com
Tue Oct 14 12:55:24 EDT 2008

```"Reasonable?".  It will solve problems where bounds will fit into an

I have modified trunk so will modify integer upper bounds if too large.

John Forrest

From:       Jan-Willem Goossens <jhmgoossens at hotmail.com>

To:         <osi at list.coin-or.org>

Date:       10/14/2008 10:42 AM

Subject:    [Osi] OsiClp branchandbound

Hi,

I understand that the "branchAndBound" method as part of
OsiClpSolverInterface is not for 'heavy' use, however:
Is it correct that OsiClp will only solve problems where the integer
variables have reasonable upper (and lower, I guess) bounds?

For example, I've tried a simple problem like   max x1 + x2, st.   x1 + 2 *
x2 <= 3.9   with x1, x2 >= 0 and integer.

NAME          BLANK
ROWS
N  OBJROW
L  R0000000
COLUMNS
C0000000  OBJROW    1.             R0000000  1.
C0000001  OBJROW    1.             R0000000  2.
RHS
RHS       R0000000  3.9
BOUNDS
UI BOUND     C0000000         1e+30
UI BOUND     C0000001         1e+30
ENDATA

This wont solve correctly

Coin0506I Presolve 0 (-1) rows, 0 (-2) columns and 0 (-2) elements
Clp0000I Optimal - objective value 3.9
Coin0511I After Postsolve, objective 3.9, infeasibilities - dual 0 (0),
primal 0 (0)
Clp0032I Optimal objective 3.9 - 0 iterations time 0.002, Presolve 0.00
Clp0006I 0  Obj 3.9 Primal inf 3.9 (1)
Clp0006I 1  Obj -0
Clp0001I Primal infeasible - objective value -0
(and stops here)

unless I add something like x1, x2 <= 10

Is this an (undocument?) requirement, or am I doing something wrong..

Thanks,

Jan-Willem Goossens

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