Dear all,

I am using lazyconstraintcallback in a C++ project. I saw there was an easy way to output nodel LP by CPXgetcallbacknodelp in C project.

Is there a similar way in a C++ project?

Thanks,

Shaon

Hi,

To Get Node LP in a C++ Project below given description: -

If by "node LP" you mean the Linear Programming (LP) relaxation solution at a node in a branch-and-bound algorithm (e.g., using a solver like SCIP, CPLEX, or Gurobi), then:

In short:

Access the current node's LP solution by querying the solver's API during the branch-and-bound process.

Typically, you retrieve variable values using functions like:

SCIPgetVarSol() for SCIP

CPXgetx() for CPLEX

GRBget() or similar for Gurobi

Example snippet in SCIP (C++) to get LP variable values at the current node:

SCIP_VAR** vars = SCIPgetVars(scip);
int nvars = SCIPgetNVars(scip);

for (int i = 0; i < nvars; ++i) {
    SCIP_Real val = SCIPgetVarSol(scip, vars[i]);  // LP value at node
    // Use val as needed
}

Thanks. I mean to get the node LP model at each node of the B&B tree.  

There is unfortunately no way to access the node LP from a callback in C++, this is only available in C. In the C interface the cplex model is given with a matrix structure using environment and lp pointers and the callback returns a pointer to the same structure. In C++ the model is given as an instance of IloModel, and there is no translation of the node lp matrix structure to an IloModel instance to give access to it.