[Scip] Branch on original variables

Wed Apr 1 16:32:19 CEST 2015

Hi,
I am now confused about how the callback methods CONSACTIVE and DEACTIVE
are supposed to work. When I create two nodes with 0 as their node
selection priority, it first goes into the left_node's consactive method,
then prop and then goes into the pricing(in my case leftnode means where
the upper bound of a variable is changed). I guess this is how it should
work.
But when I set the node selection priority of the right_node to sth larger,
it first visits the right node, after implementing consactive and prop, it
goes into DEactive method, and after that implements active and prop of the
left_node! Then goes ahead with the pricing! Does this mean that there is
sth wrong with my implementation?

Thanks in advance.

On Mon, Mar 30, 2015 at 2:07 PM, Bahareh Eghtesadi <b.eghtesadi at gmail.com>
wrote:

> Hello again,
>
> That problem is solved. Actually I was following the Binpacking example,
> so I had also added SCIPreleasecons() in the branching rule after calling
> SCIPaddconsnode(). But when I remove that, SCIPconshdlrGetConss(conshdlr)
> returns the constraints. I am wondering how come it works in the example?
> However, after I get the conss in the pricing, I loop over all of them to
> see which one is active (using SCIPconsIsActive) to apply the branching
> decisions,but non of them is active. I have checked in the conshdlr, after
> going into the CONSACTIVE , it also goes into the CONSDEACTIVE method,
> and then returns to the pricing. I suspect this may be the reason that the
> constraint is not active? or this is how it should be performed?
>
> Thanks.
>
> On Mon, Mar 30, 2015 at 2:51 AM, Gerald Gamrath <gamrath at zib.de> wrote:
>
>>  Dear Bahareh,
>>
>> do you also add the constraint via SCIPaddCons() or (better in your case)
>> SCIPaddConsNode()?
>>
>> Best,
>> Gerald
>>
>>
>> Am 30.03.2015 um 07:48 schrieb Bahareh Eghtesadi:
>>
>>   Hi Gerald,
>>
>>  Thanks for your explanation. I now understand how these constraints
>> work. So they are not basically added to the subproblems causing additional
>> constraints(which I was trying to avoid).
>>  So I am now creating two child nodes using SCIPcreatechild, then create
>> the constraint of the conshdlr and add them to the node by SCIPaddconsnode.
>>  After one iteration, when one constraint is added to a node,and the prop
>> is done , it goes in the pricing(to see if any cons is active and if so
>> change bounds), but SCIPconshdlrGetConss(conshdlr) returns no constraint! I
>> have checked  the conshdlr is found by SCIPfindConshdlr, and it is the one
>> attached to the node. Is there a way to check if the constraint is being
>> created? because the SCIPcreatecon seems to be working fine, and I have no
>> other idea why it can happen.
>>  I would appreciate your suggestions.
>>
>>  Thanks.
>>
>> On Thu, Mar 19, 2015 at 8:00 AM, Gerald Gamrath <gamrath at zib.de> wrote:
>>
>>>  Dear Bahareh,
>>>
>>> you say that you store corresponding bounds and other information in the
>>> consdata and use the CONSACTIVE method to apply them in the pricer data.
>>> Both of this uses a (set of) constraints, not just the constraint handler.
>>> Of course, within the constraint handler, you define how the data of a
>>> single constraint should look like and what should be done if the
>>> constraint is activated. So I don't really get your question, you are
>>> already using constraints...
>>>
>>> I don't see how you could have the information about bound changes for
>>> each node other than by storing them in constraints sticked to nodes. You
>>> might store all this in the constraint handler data, but you would then
>>> need to keep track of all created nodes and store a "copy" of the tree
>>> there, which is not convenient.
>>> Also the CONSACTIVE callback is not called if no constraint is
>>> activated...
>>>
>>> So I think there is no easy way to do this without creating constraints.
>>>
>>> Best,
>>> Gerald
>>>
>>>
>>> Am 18.03.2015 um 19:02 schrieb Bahareh Eghtesadi:
>>>
>>> Hi Stephen,
>>>
>>>  Thank you for your response.
>>> Actually I have been looking at the Bin Packing example. Here is what I
>>> have done so far: In my branching rule, I choose which pricing variable to
>>> branch on, create two nodes and store the corresponding bounds and other
>>> information in the consdata for each node. In the conshdlr,  in
>>> CONSACTIVE method, I change the bounds stored in the pricer data.
>>> Do I still have to create the constraint of constraint handler in each
>>> node? Because I do not have any constraint in fact, I am using the handlr
>>> to apply changes to my pricer data(bounds). I set the NEEDSCONS flag to
>>> False, and was hoping that it would be enough.
>>> Also, in this case I would not need to check whether the "cons" is
>>> active in my variable pricer. Is this right?
>>> I appreciate your help. This is my first experience with SCIP, and I am
>>> afraid I have oversimplified everything.
>>>
>>>
>>>  Thanks.
>>>
>>> On Wed, Mar 18, 2015 at 8:42 AM, Stephen J Maher <maher at zib.de> wrote:
>>>
>>>> Hi Bahareh,
>>>>
>>>> Branching on original variables can be performed similar to the way
>>>> used for branching on constraints, i.e. Ryan-Foster branching.
>>>>
>>>> In order to implement this type of branching you will need to write
>>>> your own constraint handler, branching rule and modify the variable pricer.
>>>> The constraint handler will take some reference to the original variable
>>>> and selected bounds as input and determine which master problem variables
>>>> satisfy this constraint based on given variable bounds. In your branching
>>>> rule, you will decide what original variable to branch on, create two
>>>> branching nodes and then add a constraint of your constraint handler to
>>>> each with appropriate bounds. In your variable pricer, it is then necessary
>>>> to check whether any constraints of this type exist at the current node and
>>>> apply the appropriate variable bounds on the original variables.
>>>>
>>>> An example of Ryan-Foster branching is given in the Bin Packing example
>>>> included with SCIP. It should be possible to use this as a guide for your
>>>> own rule branching on original variables.
>>>>
>>>> Cheers,
>>>>
>>>> Stephen
>>>>
>>>>
>>>> On 13/03/15 07:14, Bahareh Eghtesadi wrote:
>>>>
>>>>>  Hi all,
>>>>>
>>>>> I am tying to implement a branch and price algorithm. I want to branch
>>>>> on the original variables that are not present in the master problem,
>>>>> and then change their bound in the pricing problems. But I am not sure
>>>>> how to do this. I think I can't use SCIPbranchvar directly from
>>>>> mybranchrule. If I use a constraint handler, I wouldn't make a
>>>>> constraint of that type (because there is no such constraint), then how
>>>>> can I include it in my branchrule?
>>>>>
>>>>>
>>>>> Thanks in advance.
>>>>>
>>>>>
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>>>
>>>
>>>
>>>  --
>>> Regards
>>> Bahareh Eghtesadi
>>>
>>>
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>>>
>>>
>>
>>
>> --
>> Regards
>> Bahareh Eghtesadi
>>
>>
>>
>
>
> --
> Regards
> Bahareh Eghtesadi
>

-- 
Regards
Bahareh Eghtesadi
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