[Cbc] CBC misses optimal solution depending on activation of cuts

[Haroldo Santos]

Dear Forrest/Ted,

I have this surprisingly small MIP (few hundred of variables and
constraints)  where CBC misses the optimal solution if I deactivate cuts.

http://www.decom.ufop.br/haroldo/files/C_I_6_4_S_1-124_1.lp

CPLEX and GLPK instantly found  the optimal solution (77) no matter if
cuts/heuristics are activated or not.

Cbc, however, found a sub-optimal solution (136 or 124, depending on the
machine) when I deactivate cuts and declares is as optimal. There are no
very large/small coefficients so this is not due to numerical instability.

cbc C_I_6_4_S_1-124_1.lp cuts off solve      (wrong result)

If I call cbc with cuts

cbc C_I_6_4_S_1-124_1.lp cuts on solve     (correct result)

Cheers,

Haroldo

-- 
=============================================================De
Haroldo Gambini Santos
Computing Department - Universidade Federal de Ouro Preto - UFOP
email: haroldo [at ] iceb.ufop.br
home/research page: www.decom.ufop.br/haroldo/

"Computer science is no more about computers than astronomy
is about telescopes." Edsger Dijkstra
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