public static double MIP_arc_based(int SAA_m, int SAA_type, int sample_size)
{
int trial_limit = sample_size;
System.Console.WriteLine("Constructing the MIP with Gurobi...");
double solution = -1;
try
{
GRBEnv env = new GRBEnv("mip1.log");
GRBModel model = new GRBModel(env);
//model.Parameters.Presolve = 1;
GRBVar[] y_j = new GRBVar[E];
GRBVar[,] x_ir = new GRBVar[N, sample_size];
System.Console.WriteLine("Creating y_i (edges)");
for (int i = 0; i < E; i++)
{
y_j[i] = model.AddVar(0.0, 1.0, 0, GRB.BINARY, "y_" + node_index[unique_arcs[i].Key.Head] + "_" + node_index[unique_arcs[i].Key.Tail]);
}
System.Console.WriteLine("Creating x_ir");
for (int i = 0; i < N; i++)
{
for (int r = 0; r < sample_size; r++)
{
x_ir[i, r] = model.AddVar(0.0, 1.0, 1.0, GRB.CONTINUOUS, "x_" + i + "_" + r);
}
}
model.ModelSense = GRB.MINIMIZE;
//----------------------------------------------------------
//--------------- create the constraints
int counter = 0;
GRBLinExpr temp_exp2;
temp_exp2 = 0.0;
System.Console.WriteLine("Starting the constraints... Total : " + (trial_limit * N + 1) + " constraints");
// exactly k initial active users
for (int i = 0; i < E; i++)
{
temp_exp2.AddTerm(1.0, y_j[i]);
}
model.AddConstr(temp_exp2 == K, "constraint_y");
temp_exp2 = 0.0;
//--- influence constraints x_i_r <= Sum_j (y_j) j in all accessing nodes to i (total of N.R constraints)
//string[] neigh_arr;
GRBLinExpr temp_exp;
int j = 0;
temp_exp = 0.0;
int counter2 = 0;
ReadData temp_arc = new ReadData();
for (int r = 0; r < trial_limit; r++)
{
for (int i = 0; i < N; i++)
{
//if (SAA_tree_list[r][i].Count > 0)
//if (x_exist[r, i] == true)
{
//x_ir[i, r] = model.AddVar(0.0, 1.0, 1.0, GRB.CONTINUOUS, "x_" + i + "_" + r);
temp_exp.AddTerm(1.0, x_ir[i, r]);
//if (SAA_tree_list[r][i].Count <= N)
{
foreach (UInt16 node in SAA_pred_list[r][i]) //my predecessors can activate me
{
var x = unique_arcs.FindIndex(a => a.Key.Head == node_set[(int)node] && a.Key.Tail == node_set[i]);
//int arcID=unique_arcs.IndexOf()
temp_exp2.AddTerm(-1, x_ir[(int)node, r]);
temp_exp2.AddTerm(1, y_j[x]);
model.AddConstr(temp_exp + temp_exp2 >= 0, "constraint_2" + (counter + 1));
temp_exp2 = 0.0;
counter++;
}
}
} //end of if for null neighbourhood
temp_exp = 0.0;
} //end of for loop for nodes
} //end of for loop for sample size R
for (int r = 0; r < trial_limit; r++)
{
for (int i = 0; i < I; i++)
{
temp_exp.AddTerm(1.0, x_ir[(int)initial_infected[i], r]);
model.AddConstr(temp_exp >= 1, "constraint_3" + (counter + 1));
temp_exp = 0.0;
}
}
//no need for this in edge blocking
//for (int i = 0; i < I; i++)
//{
// temp_exp.AddTerm(1.0, y_j[(int)initial_infected[i]]);
// model.AddConstr(temp_exp == 0, "constraint_3" + (counter + 1));
// temp_exp = 0.0;
//}
model.Write("model.lp");
//model.Write("modelGRB2" + SAA_m + ".mps");
//model.Write("modelGRB2" + SAA_m + ".lp");
GRBModel p = model.Presolve();
p.Write("presolve.lp");
model.Optimize();
if (model.Status == GRB.Status.OPTIMAL)
{
Console.WriteLine("Obj: " + model.Get(GRB.DoubleAttr.ObjVal));
solution = model.Get(GRB.DoubleAttr.ObjVal);
List <UInt16> SAA_sample_result = new List <UInt16>(K);
int isfractional = 0;
result_set = new List <ushort>();
for (int jj = 0; jj < y_j.Count(); ++jj)
{
if (y_j[jj].X > 0.001)
{
//result_set.Add(node_set[jj]);
result_set.Add(node_set[jj]);
SAA_sample_result.Add((UInt16)jj);
System.Console.WriteLine(y_j[jj].VarName + "=" + y_j[jj].X);
if (y_j[jj].X < 0.9)
{
System.Console.WriteLine("Fractional value found");
System.Console.ReadKey();
isfractional = 1;
}
}
}
if (isfractional == 1)
{
System.Console.WriteLine("To conitnue click...");
System.Console.ReadKey();
}
SAA_list.Add(SAA_sample_result);
}
else
{
Console.WriteLine("No solution");
solution = 0;
}
// Dispose of model and env
model.Dispose();
env.Dispose();
}
catch (GRBException e)
{
Console.WriteLine("Error code: " + e.ErrorCode + ". " + e.Message);
}
return(solution);
}
