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Haroldo,<br>
<br>
Thanks for finding this. Because only one variable had a cost, Cbc
decides in its wisdom that it is worth trying strong branching on
that variable even if it is satisfied. This got into a part of the
code where it expects ceil(value)-value to be nonzero and bad things
happened.<br>
<br>
Should be fixed in trunk and 2.7<br>
<br>
John Forrest<br>
<br>
On 19/10/11 21:31, Haroldo Santos wrote:
<blockquote
cite="mid:CACO7Fp0TzUQjv2Mwh0Zmoy-kGr5M8tB3Q7m5fx6n0CM9bS+q8g@mail.gmail.com"
type="cite"><font face="arial,helvetica,sans-serif">Dear
Forrest/Ted,<br>
<br>
I have this surprisingly small </font><font
face="arial,helvetica,sans-serif">MIP</font><font
face="arial,helvetica,sans-serif"> (few hundred of variables and
constraints) where CBC misses the optimal solution if I
deactivate cuts.<br>
<br>
<a moz-do-not-send="true"
href="http://www.decom.ufop.br/haroldo/files/C_I_6_4_S_1-124_1.lp">http://www.decom.ufop.br/haroldo/files/C_I_6_4_S_1-124_1.lp</a><br>
<br>
CPLEX and GLPK instantly</font><font
face="arial,helvetica,sans-serif"> </font><font
face="arial,helvetica,sans-serif">found the optimal solution
(77) no matter if cuts/heuristics are activated or not.<br>
<br>
Cbc, however, found a sub-optimal solution (136 or 124,
depending on the machine) when I deactivate cuts and declares is
as optimal. </font><font face="arial,helvetica,sans-serif">There
are no very large/small coefficients so this is not due to
numerical instability.</font><br>
<font face="arial,helvetica,sans-serif"><br>
cbc C_I_6_4_S_1-124_1.lp cuts off solve (wrong result)<br>
<br>
If I call cbc with cuts<br>
<br>
</font><font face="arial,helvetica,sans-serif">cbc
C_I_6_4_S_1-124_1.lp cuts on solve (correct result)</font><br>
<br>
Cheers,<br>
<br>
Haroldo<br clear="all">
<br>
-- <br>
=============================================================De<br>
Haroldo Gambini Santos<br>
Computing Department - Universidade Federal de Ouro Preto - UFOP<br>
email: haroldo [at ] <a moz-do-not-send="true"
href="http://iceb.ufop.br" target="_blank">iceb.ufop.br</a><br>
home/research page: <a moz-do-not-send="true"
href="http://www.decom.ufop.br/haroldo/" target="_blank">www.decom.ufop.br/haroldo/</a><br>
<br>
"Computer science is no more about computers than astronomy <br>
is about telescopes." Edsger Dijkstra<br>
<br>
<br>
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<br>
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