Using a solution from a model as an input to another one and Outputting each Solution Separately - iteration

Question

I'm solving an optimization problem in which I need the result from one model to be used as a input in another model for 180 iterations. I'm using CPLEX with OPL language without any addon.
I tried to save the values from one model into an Excel file and reading those into the next model but since I'm going to do this 180 times I am worried I will make an error and have to restart or not even know I made an error.
Is it possible to have this run for 180 iterations and input each iteration's solution separately?

Answer 1

You can rely on warmstart for that.
2 simple examples in easy OPL
Warm start from a file:
include "zoo.mod";
main {
var filename = "c:/temp/mipstart.mst";
thisOplModel.generate();
cplex.readMIPStarts(filename);
cplex.solve();
writeln("Objective: " + cplex.getObjValue());
}
or with API
int nbKids=300;
// a tuple is like a struct in C, a class in C++ or a record in Pascal
tuple bus
{
key int nbSeats;
float cost;
}
// This is a tuple set
{bus} pricebuses=...;
// asserts help make sure data is fine
assert forall(b in pricebuses) b.nbSeats>0;assert forall(b in pricebuses) b.cost>0;
// To compute the average cost per kid of each bus
// you may use OPL modeling language
float averageCost[b in pricebuses]=b.cost/b.nbSeats;
// Let us try first with a naïve computation, use the cheapest bus
float cheapestCostPerKid=min(b in pricebuses) averageCost[b];
int cheapestBusSize=first({b.nbSeats | b in pricebuses : averageCost[b]==cheapestCostPerKid});
int nbBusNeeded=ftoi(ceil(nbKids/cheapestBusSize));
float cost0=item(pricebuses,<cheapestBusSize>).cost*nbBusNeeded;
execute DISPLAY_Before_SOLVE
{
writeln("The naïve cost is ",cost0);
writeln(nbBusNeeded," buses ",cheapestBusSize, " seats");
writeln();
}
int naiveSolution[b in pricebuses]=
(b.nbSeats==cheapestBusSize)?nbBusNeeded:0;
// decision variable array
dvar int+ nbBus[pricebuses];
// objective
minimize
sum(b in pricebuses) b.cost*nbBus[b];
// constraints
subject to
{
sum(b in pricebuses) b.nbSeats*nbBus[b]>=nbKids;
}
float cost=sum(b in pricebuses) b.cost*nbBus[b];
execute DISPLAY_After_SOLVE
{
writeln("The minimum cost is ",cost);
for(var b in pricebuses) writeln(nbBus[b]," buses ",b.nbSeats, " seats");
}
main
{
thisOplModel.generate();
// Warm start the naïve solution
cplex.addMIPStart(thisOplModel.nbBus,thisOplModel.naiveSolution);
cplex.solve();
thisOplModel.postProcess();
}