[Dip] Differences between GAP examples

[Matthew Galati]

Sure that can happen. It just means that the PC relaxation is too weak and
that is a bad way to solve the problem. Is that with the KP oracle or the
AP oracle? I would expect the bound using the KP oracle to be strong.

If you get 1693 with doDirect or doCut but 1698 with CBC, then either (a)
there is a bug, or (b) you are not creating the same model.

On Wed, Jun 12, 2019 at 4:14 PM Florian Fontan <dev at florian-fontan.fr>
wrote:

> Indeed! I didn't think to look there.
>
> I managed to compile the GAP example. I tested on instance a05100. This
> instance is solved optimally by a naive implementation in CBC in 0.005s.
> The optimal value is 1698 which is actually also the upper bound from the
> linear relaxation. When I try the GAP implementation given as example in
> Dip on this instance (./decomp_gap --param gap.parm)
>
>    - with doPriceCut = 1, doCut = 0, doDirect = 0: the lower bound found
>    is 1556, no feasible solution is found and the algorithm doesn't terminate
>    after at least several minutes
>    - with doPriceCut = 0, doCut = 1, doDirect = 0 or doDirect = 1: the
>    algorithm terminates very quickly, returning a best lower bound and a best
>    upper bound of 1693. I think it may be the solution of the problem with the
>    capacity constraints removed.
>
> Is this the expected behavior?
>
> Florian
> Le 11/06/2019 à 22:34, Matthew Galati a écrit :
>
> The Makefile gives some hints... one case using the built-in MILP solver,
> one case uses a KP solver.
>
> #PC: oracle for KP solve is Pisinger, BranchEnforceInMaster
> OBJS += GAP_DecompApp. at OBJEXT@
> CFLAGS = -DVERSION1
> #TODO: BranchEnforceInSubProb using GAP_DecompApp2 or by option
> # CPM/PC: built-in MILP solver, dense model build
> # BranchEnforceInMaster or BranchEnforceInSubProb by option
> #OBJS += GAP_DecompApp3. at OBJEXT@
> #CFLAGS += -DVERSION3
> # CPM/PC: built-in MILP solver, sparse model build
> # BranchEnforceInMaster or BranchEnforceInSubProb by option
> #OBJS += GAP_DecompApp4. at OBJEXT@
> #CFLAGS += -DVERSION4
>
> On Tue, Jun 11, 2019 at 3:41 PM Florian Fontan <dev at florian-fontan.fr>
> wrote:
>
>> Dear Dip community,
>>
>> I am trying to get familiar with Dip and understand how it works. Could
>> someone tell me the differences between the multiple DecompApp
>> implementation examples for the Generalized Assignment Problem?
>> https://github.com/coin-or/Dip/tree/master/Dip/examples/GAP
>>
>> For example, in GAP_DecompApp.cpp, I noticed that the setModelRelax call
>> passes NULL as first argument:
>>
>>      setModelRelax(NULL, modelName, i);
>>
>> whereas in GAP_DecompApp3.cpp, an other model is defined:
>>
>>      status = createModelPartKP(modelRelax, i);
>>      modelName = "KP" + UtilIntToStr(i);
>>      setModelRelax(modelRelax, modelName, i);
>>
>> What does that mean? I haven't found any documentation about it
>>
>> Florian
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>>
>
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