Originally posted by: LaylaM

Hello everyone!

I see an error whilst executing CPLEX+Java: 

#
# A fatal error has been detected by the Java Runtime Environment:
#
#  EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x00007fff6096c79d, pid=7256, tid=5548
#
# JRE version: Java(TM) SE Runtime Environment (10.0+46) (build 10+46)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (10+46, mixed mode, tiered, compressed oops, g1 gc, windows-amd64)
# Problematic frame:
# C  [cplex1280remotejni.dll+0x39c79d]
#
# No core dump will be written. Minidumps are not enabled by default on client versions of Windows
#
# An error report file with more information is saved as:
# C:\Users\Layla\IdeaProjects\metamodel\hs_err_pid7256.log
#
# If you would like to submit a bug report, please visit:
#   http://bugreport.java.com/bugreport/crash.jsp
# The crash happened outside the Java Virtual Machine in native code.
# See problematic frame for where to report the bug.
#

The problem occurs inside a Lazy Constraint Callback which contains a function with which I generate a schedule (s) from routing variables (x). The problem occurs during executing "model2.solve()". 

private double[] setSFromX() {
    double[] retArray = new double[noLocations];
    try {
        IloCplex model2 = new IloCplex();
        IloNumVar[] sNew = new IloNumVar[noLocations];
        for (int i = 0; i<noLocations; i++) {
            sNew[i] = model2.numVar(0.0,tmax);
        }

        IloLinearNumExpr obj = model2.linearNumExpr();
        for (int i = 0; i<noLocations; i++) {
            obj.addTerm(sNew[i],1.0);
        }
        model2.addMinimize(obj);

        for(int i = 0; i<noLocations; i++) {
            for (int j = 0; j<noLocations; j++) {
                double xij = this.getValue(x[i][j]);
                if (xij > 0.9) {
                    IloLinearNumExpr expr = model2.linearNumExpr();
                    expr.addTerm(s[j],1.0);
                    expr.addTerm(s[i],-1.0);
                    model2.addGe(expr,1.0);
                }
            }
        }

        if (model2.solve()) {
            retArray = model2.getValues(sNew);
        }
    } catch (IloException e) {
        e.printStackTrace();
    }
    return retArray;
}

So my first question: Is it possible to nest a second model (model2) inside a lazy constraint of a first model (which is referenced as "this" in the callback)? 

Second: How can I make this run? Or should I externalize the second model to another class?

Thank you :)

Layla

First question: Yes, creating and running a model inside a callback should work

Second question: In lines 21 and 22, you are working with s[] rather than sNew[]. Since the code compiled, I'm guessing s[] exists in a global context. So you're trying to add to model2 constraints involving something that does not belong to model2. I would expect that to throw an exception before getting to the solve command, but maybe not. It definitely appears wrong, though.

Using variables from model1 in model2 is illegal (like Paul suspected) but will unfortunately not throw an exception. Instead it results in undefined behavior which can itself manifest in a crash but can also go completely unnoticed.

Also note that there is a function IloCplex.numVarArray() that creates an array of variables. That is faster than the loop you use.

Originally posted by: LaylaM

Thanks Paul and Daniel, using s instead of sNew was a mistake, I corrected it and the code is running properly now ...