public OrToolsMilpSolver(int integerWidth, double epsilon = 0.000000001, string solverName = "CBC_MIXED_INTEGER_PROGRAMMING") : base(integerWidth, epsilon)
{
Solver = Solver.CreateSolver("OrTools", solverName);
}
public ProblemSolution Solve(ProblemConfiguration config)
{
var res = new ProblemSolution();
//https://developers.google.com/optimization/mip/mip_var_array#c_1
if (config.AvailableAmount <= 0)
{
throw new ArgumentException("Invalid configuration - Available amount");
}
if (config.Products == null || config.Products.Count == 0)
{
throw new ArgumentException("Invalid configuration - Products");
}
// [START solver]
// Create the linear solver with the CBC backend.
Solver solver = Solver.CreateSolver(/*"SimpleMipProgram",*/ "CBC");
// [END solver]
// [START variables]
// x, y and z are integer non-negative variables.
var variables = new List <Variable>();
foreach (var p in config.Products)
{
var variable = solver.MakeIntVar(0.0, double.PositiveInfinity, GetVariableName(p));
variables.Add(variable);
if (p.MaxUnits == 0)
{
solver.Add(variable == 0);
}
else if (
(p.MinUnits >= 0 && p.MaxUnits > 0 && p.MinUnits < p.MaxUnits) ||
(p.MaxUnits == p.MinUnits && p.MaxUnits > 0)
)
{
// other constraints
solver.Add(variable >= p.MinUnits);
solver.Add(variable <= p.MaxUnits);
}
}
res.TotalVariables = solver.NumVariables();
// [END variables]
// [START constraints]
// (unitPriceX * x) + (unitPriceY * y) + (unitPriceZ *z) <= maxValue.
var c = solver.MakeConstraint(0, config.AvailableAmount);
int i = 0;
foreach (var variable in variables)
{
c.SetCoefficient(variable, (double)config.Products[i].UnitPrice);
i++;
}
res.TotalConstraints = solver.NumConstraints();
// [END constraints]
Objective objective = solver.Objective();
i = 0;
foreach (var variable in variables)
{
objective.SetCoefficient(variable, (double)config.Products[i].UnitPrice);
i++;
}
objective.SetMaximization();
// [START solve]
Solver.ResultStatus resultStatus = solver.Solve();
// [END solve]
// [START print_solution]
// Check that the problem has an optimal solution.
if (resultStatus != Solver.ResultStatus.OPTIMAL)
{
res.HasOptimalSolution = false;
return(res);
}
res.HasOptimalSolution = true;
res.FinalAmount = (decimal)solver.Objective().Value();
res.RemainingAmount = Math.Round(config.AvailableAmount - (double)res.FinalAmount, 2);
i = 0;
foreach (var variable in variables)
{
var itemValue = variable.SolutionValue() * (double)config.Products[i].UnitPrice;
itemValue = Math.Round(itemValue, 2);
res.ResponseVariables.Add(
new SolutionVariable()
{
Name = config.Products[i].Name, //variable.Name(),
Code = config.Products[i].Code,
SolutionValue = variable.SolutionValue(),
UnitPrice = config.Products[i].UnitPrice,
FinalAmount = itemValue,
Description = variable.Name(),
Details =
$"{variable.Name()} = {variable.SolutionValue()} /// {variable.SolutionValue()} * {config.Products[i].UnitPrice} = {itemValue} euros "
});
i++;
}
res.SolveTimeMs = solver.WallTime();
res.Iterations = solver.Iterations();
res.Nodes = solver.Nodes();
return(res);
}
