public static double ComputePortfolioMinimumVariance(LabeledMatrix <Security> matrix, double expectedReturn, out Dictionary <Security, double> weights, bool allowShortSelling = false)
{
SolverContext context = SolverContext.GetContext();
Model model = context.CreateModel();
// since the row securities are the same as the column securities. use row.
var securities = matrix.RowEntities;
var weightDecisions = new Dictionary <Security, Decision>();
var rangeOfWeights = allowShortSelling ? Domain.RealRange(-10, 10) : Domain.RealRange(0, 10);
Term t1 = 0d; // constraint 1, sum of weights = 1
Term t2 = 0d; // constraint 2, expected portfolio return (sum of weight*price) = expectedReturn
foreach (var security in securities)
{
var securityWeightDecision = new Decision(rangeOfWeights, security.Symbol); // -10 <= w <= 10
weightDecisions[security] = securityWeightDecision;
model.AddDecisions(securityWeightDecision);
t1 += securityWeightDecision;
t2 += (securityWeightDecision * security.MarketPrice);
}
model.AddConstraint("SumOfWeights", t1 == 1d);
model.AddConstraint("ExpectedPortfolioReturn", t2 == expectedReturn);
// goal 1, the ptf var to be minimized
Term varianceTerm = 0d;
foreach (Security rowEntity in matrix.RowEntities)
{
foreach (Security columnEntity in matrix.ColumnEntities)
{
varianceTerm += (matrix.Get(rowEntity, columnEntity) * weightDecisions[rowEntity] * weightDecisions[columnEntity]);
}
}
Goal goal = model.AddGoal("MeanVariance", GoalKind.Minimize, varianceTerm);
var gurobiDirective = new GurobiDirective();
//gurobiDirective.OutputFlag = true;
context.Solve(gurobiDirective);
//Report report = solution.GetReport();
//Console.WriteLine("{0}", report);
//Console.WriteLine(goal.ToDouble());
//foreach (var weightDecision in weightDecisions)
//{
// Console.WriteLine(weightDecision.Key.Symbol + ":" + weightDecision.Value.GetDouble());
//}
context.ClearModel();
weights = weightDecisions.ToDictionary(p => p.Key, p => p.Value.GetDouble());
return(goal.ToDouble());
}
public static double ComputePortfolioVariance(LabeledMatrix <Security> matrix, Dictionary <Security, double> weights)
{
var sum = 0d;
foreach (Security rowEntity in matrix.RowEntities)
{
foreach (Security columnEntity in matrix.ColumnEntities)
{
sum += (matrix.Get(rowEntity, columnEntity) * weights[rowEntity] * weights[columnEntity]);
}
}
return(sum);
}