Microsoft Solver Foundation模运算符

Question

I'm trying to add a basic constraint to my solver foundation by doing the following:

model.AddConstraint("c1", x % y == 0);

I get a compile error saying "Operator '%' cannot be applied to operands of type 'Microsoft.SolverFoundation.Services.Decision' and 'Microsoft.SolverFoundation.Services.Decision'".

This makes sense since a lot of operators aren't supported. However, a lot of the operators that aren't supported (sin, cos, tan, etc.) are available as specific methods on the Model class such as below:

model.AddConstraint("c1", Model.Sum(x,y) == 0);

If I replace "Sum" with "Mod", there is no method available.

Any ideas on how to perform a modulo operation in Solver Foundation? According to the documentation here , it is supported.

I am going to start using reflector to dig through the code, but I figured I would post it on here also. If I find a solution, I will update my question to include the answer.

Answer 1

I don't see Mod at http://msdn.microsoft.com/en-us/library/ff525341(v=vs.93).aspx , but here's a workaround:

Model.Floor(Model.Quotient(x,y))==Model.Ceiling(Model.Quotient(x,y))

This is only true if x/y is an integer, and so x%y==0.

There are also other ways of combining the allowed operators to check if it is divisible. My favorite (though I wouldn't recommend it because of floating point precision) is

Model.Sin(Math.PI*Model.Quotient(x,y))==0 

Answer 2

Really interesting, I wanted to write the exact same question at SO :-)

I found out that a Mod operator is defined for the OML language at http://msdn.microsoft.com/en-us/library/ff818505(v=vs.93).aspx .

There is an overload of the AddConstraint method, that accepts an expression string(I guess an OML expression?) instead of the Term. Unfortunately, I don't know the right formatting, but once we get the knack out of it, we would be able to use all of the other operators as well.

EDIT

It looks like not every OML expression described in API is working. For example,

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

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

m.AddConstraint(null, "a > 0");
m.AddConstraint(null, "b == Plus[a,2]");

The Plus[x,y] in this case is working and the solver computes the following decision

a: 1, b: 3

But if I replace the last constraint with this one

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

I get an OmlParseException ("Failed to parse OML model. Expression: Mod[a,2]."). I guess we are on our own here and purhaps the best thing we can do is sticking with the answer of user141603.