[SCIP] Detect a feasible LP node with infeasible values

[Wen-Yang Ku]

Dear SCIP Community,

I have developed a constraint handler to ensure that an integer  
variable does not take a list of specific integer values as its  
solution. In the CONSENFOLP function, I first check if the LP solution  
of this integer variable is on the list. If it's on the list, then I  
return SCIP_INFEASIBLE. However sometimes I will run into a situation:  
"ERROR: LP was solved, all integers fixed, some constraint still  
infeasible, but no branching could be created!". I looked at solver.c  
and it seems that a feasible LP solution with all integer values fixed  
has to be feasible. So I am wondering if there is a way to detect such  
a LP node so I can cut it off and avoid the error. I currently tried  
to detect such nodes with SCIPgetNLPBranchCands(scip)==0 and count the  
number of the variables that are fixed to integers, but it gives me  
more nodes than what I expected.

Thank you very much.

Best regards,
Wen-Yang