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<div class="moz-cite-prefix">Stefan,<br>
<br>
It is a bug, but I am not sure how to fix.<br>
<br>
The optimal continuous solution is 0.0,1.0e-9,0.0. These values
are all within integer tolerances so it sets to integers i.e.
0,0,0 and thinks that as the continuous solution is integral then
the search is over and fixes integer variable to 0 and leaves
others . However while the continuous objective value was
9.0e-10, the new solution will be 1.0e-3,0.0,0.0 - giving an
objective value of 1000.<br>
<br>
The fixes that I can think of would affect performance too much
and/or be complicated.<br>
On 16/11/16 09:09, Stefan Hacker wrote:<br>
</div>
<blockquote
cite="mid:CAH=aG23GbTTGWSz7otxmOj0QuE7TkJsEyB5Rm_z8gvMQh8hePQ@mail.gmail.com"
type="cite">
<pre wrap="">Hi,
I am trying to use Cbc to solve what I thought to be a simple problem.
However the behavior I see makes me wonder if I am encountering a Cbc
bug or if there is something wrong in the way I am using it.
If I run the attached model using Cbc 2.9.7 (version isn't that
important I think) from the console like this:
cbc model.lp -solve
I get the expected objective value of 0.9. However without presolving enabled
cbc model.lp -preprocess off -solve
Cbc returns an objective value of 1000 which is incorrect.
Originally I was using Cbc as a library (close to the minimum.cpp
example from the documentation) and didn't consider presolve to be
relevant for such a small problem. Activating it feels like I am just
suppressing a symptom without understanding or fixing the cause. Even
more confusing to me is that after the call to branchAndBound the
CbcModel returns 0 for primary and secondary status and
isProvenOptimal returns true.
Is the result being wrong without presolve a bug or am I trying
something stupid here without noticing? Also Cbc returning "optimal"
in all ways I know to check but still returning an incorrect result is
unsettling. Did I miss some indicator Cbc gave me?
Thanks a lot.
Regards,
Stefan
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