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javacplex

Cplex get coefficients of objective function

I have an IloCplex object and I want to get the coefficients of the IloObjective with the Cplex Java api.

With this code I get the IloObjective and IloNumExpr but I can't access the coefficients.

IloCplex cplex = new IloCplex();
cplex.importModel("model.lp");
IloObjective obj = cplex.getObjective();
IloNumExpr expr = obj.getExpr();

How can I get the coefficients of IloObjective or IloNumExpr?

Solution

  • Since your model.lp file contains a linear model, expr should be an instance of IloLinearNumExpr, and you should be able to iterate over it using the linearIterator method:

    if (expr instanceof IloLinearNumExpr) {
    IloLinearNumExpr lexpr = (IloLinearNumExpr) expr;

    IloLinearNumExprIterator it = lexpr.linearIterator();

    while (it.hasNext()) {
        IloNumVar var = it.nextNumVar();
        double coeff = it.getValue();
        System.out.println(var + " " + coeff);
    }
}