[Scip] Add and delete variable in probing

[Gerald Gamrath]

Hi Jonas,

yes, if you want to both tighten and relax constraints, adding the slack 
variables explicitly does not help, this would only work for only 
tightening the constraints.

Using the diving mode is no option? Because changing the lhs and rhs of 
constraints would be possible there.

Perhaps we can discuss in a private mail what exactly you want to do, 
how you want to decide which constraints to tighten or to relax, and how 
me might make this possible.

Best,
Gerald


Am 17.01.2014 11:32, schrieb Jonas Witt:
> Hi Gerald,
>
> I want both tighten and relax the constraints. If I added the 
> auxiliary variables before probing, I would have to fix them to zero, 
> because otherwise I would relax the constraints in my initial problem.
>
> I search for different basic feasible solutions in the dual problem of 
> the initial LP relaxation. I create a random objective function for 
> the dual problem and I want to find a basic feasible solution which 
> optimizes this random objective function. Therefore, I solve the 
> corresponding primal problem which constraints have different right 
> hand sides and left hand sides with reference to the initial LP 
> relaxation.
>
> Best regards,
> Jonas
>
>
> On 01/17/2014 09:49 AM, Gerald Gamrath wrote:
>> Hi Jonas,
>>
>> do you want to tighten the constraints or relax them? If you only 
>> want to tighten them, I would suggest you just add the variables at 
>> the beginning, and then tighten the bounds of the auxiliary variables 
>> during probing, which will automatically be undone later.
>>
>> If you want to relax the constraints, can you explain why you want to 
>> do this?
>>
>> Currently, variables priced during probing mode are not automatically 
>> deleted after the probing node was processed, but this could probably 
>> be added, even if it does not guarantee that the variable is really 
>> deleted (you cannot delete it if the variable already occurs in some 
>> global data like a solution or conflict.
>>
>> Best,
>> Gerald
>>
>> Am 10.01.2014 15:12, schrieb Jonas Witt:
>>> Hi all,
>>>
>>> I want to change the rhs/lhs of some constraints during probing (it 
>>> has to be probing not diving!). Since this is not possible, I would 
>>> like to add a new variable to each constraint which I want to 
>>> change. Then I want to fix this variable in probing mode via 
>>> SCIPfixVarProbing(), which implicitly changes the rhs and lhs of the 
>>> constraint. In the end I want to solve the probing LP, exit the 
>>> probing mode and delete the created variables.
>>>
>>> How can I achieve this? Should I mark the variables to be deletable 
>>> by SCIPvarMarkDeletable() and add the variables to the problem 
>>> during probing in order to automatically delete the variables after 
>>> the probing node was processed?
>>>
>>> Best regards,
>>> Jonas
>>> _______________________________________________
>>> Scip mailing list
>>> Scip at zib.de
>>> http://listserv.zib.de/mailman/listinfo/scip
>>
>> _______________________________________________
>> Scip mailing list
>> Scip at zib.de
>> http://listserv.zib.de/mailman/listinfo/scip
>
> _______________________________________________
> Scip mailing list
> Scip at zib.de
> http://listserv.zib.de/mailman/listinfo/scip