Question

Do anyone know any simple solver that can solve linear constraint math models? Example a simple model:

a + b + c = 100;
a/b/c = 2/3/4;
a > d

I’m using MS Solver foundation and this is my C# code, but it throw UnsolvableModelException:

        SolverContext solverContext = SolverContext.GetContext();
        Model model = solverContext.CreateModel();
        Decision a = new Decision(Domain.Real, "a");
        Decision b = new Decision(Domain.Real, "b");
        model.AddDecisions(a, b);
        model.AddConstraint("fator", a / b ==  4);
        model.AddConstraint("sum", a + b == 5);
        Solution solution = solverContext.Solve(new ConstraintProgrammingDirective());
        Report report = solution.GetReport();
        Console.WriteLine("a = {0} ; b = {1}", a, b);

Thanks for any help

Edit:

Because int CSP(constraint sstisfaction programming) problem, you shouldn’t use any Directive when solving it.
The code should be:

    SolverContext solverContext = SolverContext.GetContext();
    Model model = solverContext.CreateModel();
    Decision a = new Decision(Domain.Real, "a");
    Decision b = new Decision(Domain.Real, "b");
    model.AddDecisions(a, b);
    model.AddConstraint("fator", a / b ==  4);
    model.AddConstraint("sum", a + b == 5);
    Solution solution = solverContext.Solve();
    Report report = solution.GetReport();
    Console.WriteLine("a = {0} ; b = {1}", a, b);

However, I don’t know why I ran to slowly I only need the first solution in the solution set.

Answer 1

Depending on your needs, Wolfram Alpha may be useful (at least for verification). I doubt you can solve complex problems, because the input is lenght-limited. But for simple problems as your example, it’s OK.

http://www.wolframalpha.com/input/?i=solve+a+%2B+b+%2B+c+%3D%3D+100%3B+a%2Fb+%3D%3D+2%2F3%3B+b%2Fc%3D%3D3%2F4%3B+a+%3E+d