[Scip] Heuristics - Shift and Propagate

[Jacob Spönemann]

  Hi all,

I implemented a column generation algorithm using SCIP and Gurobi.

I am running into problems when the heuristic "Shift and Propagate" is 
executed (in the end convertSides in lpi_grb.c causes the error because 
the Gurobi interface cannot handle ranged rows). I tried to disable the 
heuristic by setting the frequency parameter to -1, but nevertheless the 
heuristic is executed.

I observed that the value of the frequency parameter is set to 0 during 
solution process. Is there any chance to prevent that?

Best regards,

Jacob

Am 31.01.2011 04:29, schrieb Stephen J Maher:
> Hi Gregor,
>
> I have been using the updated file that you sent to me. It worked well.
>
> Unfortunately I am having another problem with the shift and propagate 
> heuristic. I have disabled it by setting the frequency parameter to 
> -1, however I am getting the error
>
> src/scip/heur_shiftandpropagate.c:1464: heurExecShiftandpropagate: 
> Assertion `SCIPisFeasEQ(scip, lb, ub)' failed
>
> Is there a way for me to avoid this error?
>
> Thanks for your help,
>
> Steve
>
>
>
> Gregor Hendel wrote:
>> Hi Steve,
>>
>> I have changed the file heur_shiftandpropagate.c, s.t. it should work 
>> now. In the attachment, you'll find the file. Just replace
>> the old version in <scip-base-dir>/src/scip by the new one. I'm not 
>> able to test it on column generation codes, so
>> please inform me if this bugfix has fixed your problem sufficiently.
>>
>>> HI Gregor,
>>>
>>> I have run my code using the debugger gdb and it seems that the 
>>> problem with this heuristic occurs when the rens heuristic is 
>>> called. The problem still exists when I disable both, the rens and 
>>> shift-and-propagate, heuristics. If I disable all of the heuristics 
>>> the problem doesn't occur.
>>>
>>> I am adding variables dynamically. I have a variable pricer that 
>>> adds variables representing network flows. I am also adding 
>>> constraints of the problem through a version of benders 
>>> decomposition. At each iteration I am removing all variables from 
>>> the master problem and reinitialising using the optimal variables 
>>> from the previous iteration.
>>>
>>> The problem is written as a MIP with the network flow variables 
>>> being binary and there is a set of continuous variables as well.
>>>
>>> Thanks a lot for your help.
>> Thank you for helping us developing a more stable SCIP version.
>>
>> Best, gregor
>
>
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