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<DIV>I’m in the process of writing an interface between the JuMP (<A
href="http://jump.readthedocs.org">http://jump.readthedocs.org</A>) modeling
language for Julia (<A href="http://julialang.org">http://julialang.org</A>) and
Optimization Services, writing OSiL files to access solvers such as Bonmin and
Couenne that are otherwise difficult to access from high-level languages right
now because they only have C++ API’s. The end result once I get everything
working should be similar to the prototype nonlinear Matlab interface I sent to
this list in October 2013, but much higher-performance thanks to Julia’s
just-in-time compilation, and fully open-source.</DIV>
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<DIV>I have a question about linear objective coefficients in OSiL. As far as I
can read the OSiL.xsd schema, there don’t appear to be any assumptions or
requirements that the indices of objective coefficients be sorted or unique.
Depending on the modeling language, it may potentially be simpler to write the
interface in such a way that the generated OSiL file directly translates
objective coefficients without combining duplicates or sorting indices. I will
have to do some testing, but should OSiL files with this irregular set of
objective coefficients be valid and work correctly, or be checked and verified
against?</DIV>
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<DIV>Based on the current code, it looks like any solvers that use
OSInstance::getDenseObjectiveCoefficients() could interpret an objective with
duplicate coefficients incorrectly. The dense coefficients are all initialized
to zero, but the = at <A
href="https://projects.coin-or.org/OS/browser/trunk/OS/src/OSCommonInterfaces/OSInstance.cpp?rev=4915#L2218">https://projects.coin-or.org/OS/browser/trunk/OS/src/OSCommonInterfaces/OSInstance.cpp?rev=4915#L2218</A>
means only the last objective coefficient with a given index will be seen by the
solver, rather than combining values with the same index. Would it make sense to
change that = to a += ?</DIV>
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<DIV>Thanks,</DIV>
<DIV>Tony</DIV>
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