Poolsearch.java
/*版权所有2023,Gurobi O狗万app足彩ptimization, LLC */ /*我们通过使用PoolSearchMode */ import Gurobi .*为给定的背包问题找到替代的ε -最优解;public class Poolsearch {public static void main(String[] args) {try{//样本数据int groundSetSize = 10;double objCoef[] = new double[] {32, 32, 15, 15, 6,6, 1,1,1,1};double knapsackCoef[] = new double[] {16,16,8,8,4,4,2,2,1,1};双倍预算= 33;int e，状态，nSolutions;//创建环境GRBEnv env = new GRBEnv("Poolsearch.log");//创建初始模型GRBModel = new GRBModel(env)model.set (GRB.StringAttr。ModelName Poolsearch); // Initialize decision variables for ground set: // x[e] == 1 if element e is chosen GRBVar[] Elem = model.addVars(groundSetSize, GRB.BINARY); model.set(GRB.DoubleAttr.Obj, Elem, objCoef, 0, groundSetSize); for (e = 0; e < groundSetSize; e++) { Elem[e].set(GRB.StringAttr.VarName, "El" + String.valueOf(e)); } // Constraint: limit total number of elements to be picked to be at most // Budget GRBLinExpr lhs = new GRBLinExpr(); for (e = 0; e < groundSetSize; e++) { lhs.addTerm(knapsackCoef[e], Elem[e]); } model.addConstr(lhs, GRB.LESS_EQUAL, Budget, "Budget"); // set global sense for ALL objectives model.set(GRB.IntAttr.ModelSense, GRB.MAXIMIZE); // Limit how many solutions to collect model.set(GRB.IntParam.PoolSolutions, 1024); // Limit the search space by setting a gap for the worst possible solution that will be accepted model.set(GRB.DoubleParam.PoolGap, 0.10); // do a systematic search for the k-best solutions model.set(GRB.IntParam.PoolSearchMode, 2); // save problem model.write("Poolsearch.lp"); // Optimize model.optimize(); // Status checking status = model.get(GRB.IntAttr.Status); if (status == GRB.INF_OR_UNBD || status == GRB.INFEASIBLE || status == GRB.UNBOUNDED ) { System.out.println("The model cannot be solved " + "because it is infeasible or unbounded"); System.exit(1); } if (status != GRB.OPTIMAL) { System.out.println("Optimization was stopped with status " + status); System.exit(1); } // Print best selected set System.out.println("Selected elements in best solution:"); System.out.print("\t"); for (e = 0; e < groundSetSize; e++) { if (Elem[e].get(GRB.DoubleAttr.X) < .9) continue; System.out.print(" El" + e); } System.out.println(); // Print number of solutions stored nSolutions = model.get(GRB.IntAttr.SolCount); System.out.println("Number of solutions found: " + nSolutions); // Print objective values of solutions for (e = 0; e < nSolutions; e++) { model.set(GRB.IntParam.SolutionNumber, e); System.out.print(model.get(GRB.DoubleAttr.PoolObjVal) + " "); if (e%15 == 14) System.out.println(); } System.out.println(); // print fourth best set if available if (nSolutions >= 4) { model.set(GRB.IntParam.SolutionNumber, 3); System.out.println("Selected elements in fourth best solution:"); System.out.print("\t"); for (e = 0; e < groundSetSize; e++) { if (Elem[e].get(GRB.DoubleAttr.Xn) < .9) continue; System.out.print(" El" + e); } System.out.println(); } model.dispose(); env.dispose(); } catch (GRBException e) { System.out.println("Error code: " + e.getErrorCode() + ". " + e.getMessage()); } } }
