[Scip] Add and delete variable in probing

[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
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