[Cbc] Intermediate results via CbcModel.bestSolution()

[Haroldo Santos]

Hi Forrest,

originalColumns() returns a primal solution ? indexes to map to the
original columns ?

On Thu, Jul 15, 2010 at 1:39 PM, John Forrest
<john.forrest at fastercoin.com> wrote:
> bestSolution() never decompressed solution so you just must have been
> lucky.
>
> If you did CglPreProcess and pass a pointer to that in to the handler
> using bestSolution() then you can pick up originalColumns() and put the
> solution back into the original model.
>
> John Forrest
>
>
>
> On Thu, 2010-07-15 at 11:27 -0400, acw at ascent.com wrote:
>> In our application, we pose biggish problems to Cbc, which then goes
>> off and spends quite a while solving them.  Even before we get the
>> optimal solution, we can make use of any solutions Cbc finds along the
>> way.
>>
>> So, during the solution process, when we see that Cbc has improved its
>> best result, we query the CbcModel using bestSolution().
>>
>> Recently we've started encountering a problem where the returned
>> solution is much shorter than expected.  Looking at the number of
>> columns in the solution makes us suspect that we are seeing solutions
>> to the processed model, and not to the original one.  That is, Cbc is
>> boiling the problem down to a smaller, equivalent problem, and solving
>> that; when it's completely finished it inverts the transformation to
>> give a solution to the original problem.  But if we interrupt it, we
>> find an intermediate solution to the transformed problem, not the
>> original.
>>
>> This makes a certain amount of sense, but it didn't use to happen.  In
>> a previous Cbc version, either the model was not compressed in the
>> same way, or bestSolution() inverted the compression regardless of
>> whether the solution was complete.
>>
>> Is this change in behavior intentional?  If so, does there remain any
>> supported way to extract an intermediate solution to the problem as
>> posed?
>>
>> Thank you; our experience with Cbc has been overwhelmingly positive,
>> and we're sure there's an easy solution to this glitch as there have
>> been for every problem we've encountered in the past.
>> _______________________________________________
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>
>
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>



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

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