[Scip] Early Branching issues
Gerald Gamrath
gamrath at zib.de
Fri Feb 8 00:19:05 MET 2013
Hi Jose,
when do you want to stop pricing and start cutting? When you are still
at the root node? In case you do it after you finished the root node,
the explanation is easy: per default, SCIP only generates cutting planes
at the root node, and even if you set the separation to aggressive,
separators will only be called every 20 depth levels. But you can change
the frequencies of the separators via the SCIP shell, you just have to
change the freq parameters of the separators. Perhaps this helps?
Best,
Gerald
Am 07.02.2013 22:29, schrieb Stefan Heinz:
> Hi Jose,
>
> can you send a statistic output of one run please.
>
> Stefan
>
>
> On 02/07/2013 07:56 PM, Jose L Walteros wrote:
>> Hi Stefan,
>>
>> Yesterday I gave up with the pricer deactivation and tried to continue
>> through the (*result= SCIP_SUCCESS) path.
>>
>>
>> This is the piece of the code I have:
>> if(nconsstree>EARLY_BRANCHING_LIMIT){
>> (*success) = TRUE;
>> for(s=0;s<n;s++)
>> {
>> for(i=0;i<m;i++)
>> {
>> SCIP_CALL( SCIPsetConsModifiable(scip, conss[s][i], FALSE) );
>> }
>> }
>> SCIP_CALL( SCIPsetSeparating(scip, SCIP_PARAMSETTING_AGGRESSIVE, TRUE) );
>> return SCIP_OKAY;
>> }
>>
>> I am positive that the constraints I am using are the transformed ones
>> because those are the ones present in the pricer's data structure and as
>> far as I know those have to be the transformed ones, otherwise I would not
>> be able to update them with new columns.
>>
>> To make sure they are the transformed ones I also tried:
>>
>> SCIP_CONS* cons;
>> if(nnodes>EARLY_BRANCHING_LIMIT){
>> (*success) = TRUE;
>> for(s=0;s<n;s++)
>> {
>> for(i=0;i<m;i++)
>> {
>> SCIP_CALL( SCIPgetTransformedCons(scip, conss[s][i], &cons ));
>> SCIP_CALL( SCIPsetConsModifiable(scip, cons, FALSE) );
>> }
>> }
>> SCIP_CALL( SCIPsetSeparating(scip, SCIP_PARAMSETTING_AGGRESSIVE, TRUE) );
>> return SCIP_OKAY;
>> }
>>
>> but no cuts are generated. I am stuck here, I will appreciate some help
>>
>> Thank for your help
>>
>>
>> On Thu, Feb 7, 2013 at 5:32 AM, Stefan Heinz <heinz at zib.de> wrote:
>>
>>> Hi Jose,
>>>
>>>
>>>
>>> On 02/07/13 04:32, Jose L Walteros wrote:
>>>
>>>> Hi Stefan,
>>>>
>>>> I was originally setting a flag inside of the pricer that acivates when
>>>> the number of nodes was above a given threshold k.
>>>> Then, once the flag was activated, I was calling:
>>>>
>>>> pricer = SCIPfindPricer(scip, PRICER_NAME);
>>>> SCIP_CALL( SCIPdeactivatePricer(scip, pricer) );
>>>> SCIP_CALL(SCIPrestartSolve(**scip) );
>>>>
>>>> for(s=0;s<n;s++)
>>>> {
>>>> for(i=0;i<m;i++)
>>>> {
>>>> SCIP_CALL( SCIPsetConsModifiable(scip, conss[s][i], FALSE) );
>>>> }
>>>> }
>>>> SCIP_CALL( SCIPsetSeparating(scip, SCIP_PARAMSETTING_AGGRESSIVE, TRUE) );
>>>>
>>>>
>>>> I was getting the following error, which I thought i was because the call
>>>> was inside the pricer:
>>>> cannot call method <SCIPdeactivatePricer> in solving stage
>>>>
>>> Instead of deactivation the pricer, just return within your pricer without
>>> doing anything and pretend that all columns/variables are generated
>>> (*result = SCIP_SUCCESS). If you are not pretending that all
>>> columns/variables are there and force an early branching, then the LP is
>>> officially not solved to optimality. Meaning that all separators are not
>>> starting since they need an optimal basis.
>>>
>>>
>>>
>>>
>>>> Then, What I tried to do then was to code an event handler that catches
>>>> and SCIP_EVENTTYPE_NODEFOCUSED
>>>>
>>>> and then deactivates the pricer. Unfortunately, I'm still getting the
>>>> same error.
>>>>
>>>> I checked the reference file and it seems that deactivate pricer can only
>>>> be called in the stages:
>>>> SCIP_STAGE_PROBLEM
>>>> SCIP_STAGE_EXITSOLVE
>>>>
>>>>
>>>> Also, If I just use in the event handler:
>>>>
>>>> for(s=0;s<n;s++)
>>>> {
>>>> for(i=0;i<m;i++)
>>>> {
>>>> SCIP_CALL( SCIPsetConsModifiable(scip, conss[s][i], FALSE) );
>>>> }
>>>> }
>>>> SCIP_CALL( SCIPsetSeparating(scip, SCIP_PARAMSETTING_AGGRESSIVE, TRUE) );
>>>>
>>> Regarding the modifiable flag. Please make sure that you change the flags
>>> of the transformed constraints and not of the original once.
>>>
>>> Best Stefan
>>>
>>>> It does not generate any cuts.
>>>>
>>>> Thanks for your help
>>>>
>>>> -Jose
>>>>
>>>>
>>>> On Wed, Feb 6, 2013 at 6:31 PM, Stefan Heinz <heinz at zib.de <mailto:
>>>> heinz at zib.de>> wrote:
>>>>
>>>> Hi Jose,
>>>>
>>>>
>>>> On 02/07/2013 12:20 AM, Jose L Walteros wrote:
>>>>
>>>> Hi Stefan,
>>>>
>>>> Thanks for your quick response, I changed the code as you
>>>> suggested (I am
>>>> also changing some other parameters and I guess I confused the
>>>> TRUE
>>>> parameter as the way to do it, thanks for the clarification)
>>>> but still no
>>>> additional cut are generated.
>>>>
>>>> I am using now:
>>>>
>>>> SCIP_CALL( SCIPsetSeparating(scip,
>>>> SCIP_PARAMSETTING_AGGRESSIVE, TRUE) );
>>>>
>>>> I also tried the default.
>>>>
>>>> For this formulation all the constraints of the master problem
>>>> are Set
>>>> Partitioning constraints defined as:
>>>>
>>>> SCIP_CALL( SCIPcreateConsBasicSetpart(**scip, &(conss[s][i]),
>>>> name, 0, NULL)
>>>> );
>>>> SCIP_CALL( SCIPsetConsModifiable(scip, conss[s][i], TRUE) );
>>>>
>>>> One think, if you stop generating new variables completely, you
>>>> should change the "modifiable" flag of the constraints to FALSE.
>>>> Additionally you could turn off your pricer(s) and force a
>>>> restart. That would run presolving for example again. Check the
>>>> method SCIPrestartSolve():
>>>>
>>>> http://scip.zib.de/doc/html/**scip_8h.shtml#**
>>>> a08e665c374c599f96c4968ce8cf10**8ba<http://scip.zib.de/doc/html/scip_8h.shtml#a08e665c374c599f96c4968ce8cf108ba>
>>>>
>>>> I am not sure but the modifiable issue can be the/a reason for not
>>>> executing the separation. Try it and if does not work, I will
>>>> check the code (during the day tomorrow).
>>>>
>>>> Best and good night Stefan
>>>>
>>>>
>>>>
>>>> I know that no separators are called because in the execution
>>>> summary the
>>>> number of calls to all separators is zero.
>>>>
>>>> Is there anything I am missing?
>>>>
>>>> Thanks
>>>>
>>>> -Jose
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> On Wed, Feb 6, 2013 at 5:53 PM, Stefan Heinz <heinz at zib.de
>>>> <mailto:heinz at zib.de>> wrote:
>>>>
>>>> Hi Jose,
>>>>
>>>> It should be possible to turn on the separation. The bool
>>>> parameter you
>>>> changed from TRUE to FALSE has nothing to with turning on
>>>> or off the "OFF"
>>>> mode.
>>>>
>>>> http://scip.zib.de/doc/html/****scip_8h.shtml#**<http://scip.zib.de/doc/html/**scip_8h.shtml#**>
>>>> af91abf95639f1bf2022c11d13a032****b10<http://scip.zib.de/doc/
>>>> **html/scip_8h.shtml#**af91abf95639f1bf2022c11d13a032**b10<http://scip.zib.de/doc/html/scip_8h.shtml#af91abf95639f1bf2022c11d13a032b10>
>>>>
>>>>
>>>> It does the parameter change "quite" or not. Meaning with
>>>> or without an
>>>> output via the message handler. You need to change the
>>>> second parameter to
>>>> one of the followings:
>>>>
>>>> * SCIP_PARAMSETTING_DEFAULT which are the default values
>>>> of all separating
>>>> parameters
>>>>
>>>> * SCIP_PARAMSETTING_FAST such that the time spend for
>>>> separating is
>>>> decreased
>>>>
>>>> * SCIP_PARAMSETTING_AGGRESSIVE such that the separating is
>>>> done more
>>>> aggregative
>>>>
>>>> * SCIP_PARAMSETTING_OFF which turn off all separating
>>>>
>>>> Probably you want to try SCIP_PARAMSETTING_DEFAULT first.
>>>>
>>>> Best Stefan
>>>>
>>>>
>>>> On 02/06/2013 09:59 PM, Jose L Walteros wrote:
>>>>
>>>> Hi all,
>>>>
>>>> I am solving a problem via Branch and Price. For one
>>>> of my experiments, I
>>>> am interested in stopping the pricing at a certain
>>>> point in the B&B tree
>>>> to
>>>> heuristically obtain a good solution. Since I am no
>>>> longer pricing new
>>>> variables, I am wondering if it is possible to
>>>> activate the separate
>>>> algorithms to add default SCIP cutting planes after no
>>>> more columns are
>>>> generated.
>>>>
>>>> I tried to play with SCIP_CALL( SCIPsetSeparating(scip,
>>>> SCIP_PARAMSETTING_OFF, TRUE) ); changing it from TRUE
>>>> to FALSE but I did
>>>> not get the expected beheavior.
>>>>
>>>> Tanks
>>>>
>>>> -Jose
>>>>
>>>>
>>>>
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>>>>
>>>>
>>>>
>>>>
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