[Scip] Tentative branching not working

[nikolaj@crt.umontreal.ca]

Hi all,

I'm using SCIP to branch and cut. In the B&C process, I use my own defined
branching rule (scip::ObjBranchrule). What I would like to do is pretty
simple but I can't get it done right in SCIP.

My branching strategy is to define two children, each with a new local
constraint on several variables. I read in this mailing list that this
could be done by defining the two constaints and adding them locally to
the children.

Here is a snipet of my code of the method scip_execlp of my branching rule :

------------------------------------------------------------------------------
SCIP_RETCODE MyOwnLittleBranchingRule::scip_execlp
(
 	    SCIP *   	 scip,
		SCIP_BRANCHRULE *  	branchrule,
		SCIP_Bool  	allowaddcons,
		SCIP_RESULT *  	result
)
{
//added constraints
SCIP_CONS * cons1;
SCIP_CONS * cons2;

//the two nodes in the B&B tree which are created
SCIP_NODE * child1;
SCIP_NODE * child2;

//find best candidate to branch on (basically, an edge of a graph).
[code omitted]

//create child 1 : serve edge from i to j
SCIP_CALL_EXC(SCIPcreateChild(scip,&child1,0.0,SCIPgetLocalOrigEstimate(scip)));
//create child 2 : serve edge from j to i
//SCIP_CALL_EXC(SCIPcreateChild(scip,&child2,0.0,SCIPgetLocalOrigEstimate(scip)));

SCIP_CALL_EXC(SCIPcreateConsLinear(scip, & cons1, "name_cons1", 0, NULL,
NULL, 1.0, 1.0,
FALSE, TRUE, TRUE, TRUE, TRUE, TRUE, FALSE, FALSE, FALSE, TRUE));

//construct the linear constraint
//loop on S,i,k, model_->y_[S][i][k] is a pointer on the right variable
[code omitted]
SCIP_CALL_EXC(SCIPaddCoefLinear(scip,cons1,model_->y_[S][i][k],1.0));

//add constraint to node
SCIP_CALL_EXC(SCIPaddConsNode(scip,child1,cons1,NULL));

//release constraint
SCIP_CALL_EXC(SCIPreleaseCons(scip,&cons1));

//the same is done for child2 with another similar linear constraint
[code omitted]

*result = SCIP_BRANCHED;

return SCIP_OKAY;
}
------------------------------------------------------------------------------

SCIP doesn't seem to take into account the added constraint.
For example, in the optimal solution of the linear relaxation of the LP at
a node with the linear constraint added, the flow is not 1 as expected
(i.e., the added constraint is violated).

The constraint added fixes the flow on an edge of a graph and is to be
kept in the search while in the subtree rooted at the nood where the cut
was added.

Any idea on what is going wrong ?

Best regards,
Nikolaj