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lpmod_cs.cs
/* Copyright 2021, Gurobi Optimization, LLC */ /* This example reads an LP model from a file and solves it. If the model can be solved, then it finds the smallest positive variable, sets its upper bound to zero, and resolves the model two ways: first with an advanced start, then without an advanced start (i.e. 'from scratch'). */ using System; using Gurobi; class lpmod_cs { static void Main(string[] args) { if (args.Length < 1) { Console.Out.WriteLine("Usage: lpmod_cs filename"); return; } try { // Read model and determine whether it is an LP GRBEnv env = new GRBEnv(); GRBModel model = new GRBModel(env, args[0]); if (model.IsMIP != 0) { Console.WriteLine("The model is not a linear program"); Environment.Exit(1); } model.Optimize(); int status = model.Status; if ((status == GRB.Status.INF_OR_UNBD) || (status == GRB.Status.INFEASIBLE) || (status == GRB.Status.UNBOUNDED)) { Console.WriteLine("The model cannot be solved because it is " + "infeasible or unbounded"); Environment.Exit(1); } if (status != GRB.Status.OPTIMAL) { Console.WriteLine("Optimization was stopped with status " + status); Environment.Exit(0); } // Find the smallest variable value double minVal = GRB.INFINITY; GRBVar minVar = null; foreach (GRBVar v in model.GetVars()) { double sol = v.X; if ((sol > 0.0001) && (sol < minVal) && (v.LB == 0.0)) { minVal = sol; minVar = v; } } Console.WriteLine("\n*** Setting " + minVar.VarName + " from " + minVal + " to zero ***\n"); minVar.UB = 0.0; // Solve from this starting point model.Optimize(); // Save iteration & time info double warmCount = model.IterCount; double warmTime = model.Runtime; // Reset the model and resolve Console.WriteLine("\n*** Resetting and solving " + "without an advanced start ***\n"); model.Reset(); model.Optimize(); double coldCount = model.IterCount; double coldTime = model.Runtime; Console.WriteLine("\n*** Warm start: " + warmCount + " iterations, " + warmTime + " seconds"); Console.WriteLine("*** Cold start: " + coldCount + " iterations, " + coldTime + " seconds"); // Dispose of model and env model.Dispose(); env.Dispose(); } catch (GRBException e) { Console.WriteLine("Error code: " + e.ErrorCode + ". " + e.Message); } } }