How to use If operator in MS Solver Foundation?

Question

What's wrong with this code?:

SolverContext sc = SolverContext.GetContext();
Model m = sc.CreateModel();

m.AddDecision(new Decision(Domain.IntegerNonnegative, "a"));
m.AddDecision(new Decision(Domain.IntegerNonnegative, "b"));

m.AddConstraint(null, "a < 2");
m.AddConstraint(null, "b == If[a == 2, 2, 1]");

var sol = sc.Solve();
Console.WriteLine(sol.GetReport());

The solver freezes and doesn't give any result. I'm playing with the If operator trying to see how it works but doesn't seem to do what I expect. Not sure I'm using it the right way (I'm trying to say, if a equals 2 then b must equal 2, otherwise 1).

I also tried

m.AddConstraint(null, "If[a == 2, b == 2, b == 1]");

with the same result.

You might also try here: http://social.msdn.microsoft.com/Forums/en-US/solverfoundation/threads — Tergiver, Jun 22 '12 at 21:15

Anders Gustafsson · Accepted Answer · 2012-06-24T20:58:42.257

It seems like the solver that is applied to this problem is hampered by the extent of the Decision domain. If you limit the domain to for example the integer range [0, 10]:

m.AddDecision(new Decision(Domain.IntegerRange(0, 10), "a"));
m.AddDecision(new Decision(Domain.IntegerRange(0, 10), "b"));

a feasible solution to the problem is generated fairly quickly. In other words, the constraint b == If[a == 2, 2, 1] is perfectly valid.

BTW, it is a little odd that you in the first constraint require that a < 2, and in the second constraint test the condition a == 2. But I assume you are in an experimentation phase right now...

How to use If operator in MS Solver Foundation?

1 Answers1