[SCIP] Branch on slack variables

[Gerald Gamrath]

Hi Wei Kai,

I'm not sure what you mean. Do you want to change a constraint from, 
say, less-equal to larger-equal? Every linear constraint in SCIP has a 
left-hand side and a right-hand side. If you have an equation, both are 
equal, if you have an inequality, either the lhs is -infinity or the rhs 
is +infinity. You can change this to adjust your constraint sense, but 
this is only allowed in the problem creation stage, once solving 
started, you cannot change the lhs or rhs of a constraint anymore - this 
constraint may have led to some nodes being cut off, you cannot just 
relax it now and expect to get the correct solution.

But if you have the slack variable explicitly in your model, you could 
just branch on it? On the other hand, you may create new linear 
constraints and add them to a local node, but not change them.

Best,
Gerald

On 12.01.2016 07:45, weikaimas at 163.com wrote:
> Hi all,
>     I implement a B&P algorithm. I consider a branching stratege base 
> on slack variables of a set of constraint.
> How can I change the sense of the constraint and record the 
> information in consdata of current node.
>
> Thank you all.
>
> Best,
> Wei kai

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