Originally posted by: SaumyaB

Hi,

I am trying to formulate a variant of RCPSP using Java and CP Optimizer where my objective is to minimize weighted number of late activities. To do so, I have a boolean variable U_i for activity i such that:

U_i := 0, if C_i ≤ d_i

and U_i := 1, otherwise

where C_i is the completion time of activity i (variable in this case) and d_i is the due date of that activity (known from data). Is there a way to formulate such an if-else condition as a logical constraint.

Any help would be greatly appreciated.

Hi

House building with earliness/tardiness costs

This is a problem of building a house; the masonry, roofing, painting, etc. must be scheduled. Some tasks must necessarily take place before others and these requirements are expressed through precedence constraints.

Moreover, there are earliness and tardiness costs associated with some tasks. The objective is to minimize these costs.

To access this example, go to: examples/opl/sched_time.

at CPLEX_Studio128\cpoptimizer\examples\src\java you have the same in java : SchedTime.java

regards

Originally posted by: SaumyaB

Hi,

Thanks for the quick response. I will try formulating with this approach.

Originally posted by: SaumyaB

Hi Alex,

While trying out the suggested approach and going through the example SchedTime.java, I notice that in the function TardinessCost, two scenarios are possible, depending upon whether or not the useFunction = 0. I am not sure in which scenarios the else condition of the function is executed (line no 52) since useFunction is set to 1 in the line 89. 

Any help on this is greatly appreciated. Thanks.

Code Snippet (from the example):

public static IloNumExpr TardinessCost(IloCP cp, IloIntervalVar task, int dd, double weight, int useFunction) throws IloException {
        if (useFunction != 0) {
            double[] arrX = {(double)dd};
            double[] arrV = {0.0, weight};
            IloNumToNumSegmentFunction f = cp.piecewiseLinearFunction(arrX, arrV, dd, 0.0);
            return cp.endEval(task,f);
        } else {
            return cp.prod(weight, cp.max(0, cp.diff(cp.endOf(task), dd)));
        }
    }

Hi,

in order to better understand you could have a look at the equivalent OPL example at CPLEX_Studio128\opl\examples\opl\sched_time

For your question, since useFunction==1

double[] arrX = {(double)dd};
            double[] arrV = {0.0, weight};
            IloNumToNumSegmentFunction f = cp.piecewiseLinearFunction(arrX, arrV, dd, 0.0);
            return cp.endEval(task,f);

is called.

regards