Getting multiple optimal solutions using MS Solver Foundation

Question

Hi everyone, i'm working on a small project to learn MS Solver Foundation. I've got an application that's supposed to accept some constraints and a goal, then display ALL the optimal solutions. This is the call that i make in order to get a solution: 

var solution = solver.Solve(new ConstraintProgrammingDirective());

However, i get the following exception (an UnsolvableModelException): "No solver could be found that can accept the model given the model type and directive(s)".

However, if i just write the code as follows i don't get an exception:

var solution = solver.Solve();

But then in this case i don't get ALL the optimal solutions, i just get one. I would like to display ALL the optimal solutions to the user.

Thanks.

Answer 1

Hi Arlvin,

Sorry to see that nobody has answered your question. For solvers that support returning more than one solution you need to call the GetNext method on the solution object:

var nextSolution = solution.GetNext();

Not all solvers support this method - in fact, the ConstraintProgramming solver might be the only one. In order to use the ConstraintProgramming solver, make sure that your model does not contain any real-valued parameters or decisions. Here is more documentation on the GetNext method:

http://msdn.microsoft.com/en-us/library/microsoft.solverfoundation.services.solution.getnext(v=vs.93)

Hope this helps, Nate