[开发工具]IDEA安装gurobi求解器，并运行官方demo。报错java.lang.UnsatisfiedLinkError解决

1.1下载gurobi求解器，https://www.gurobi.com/downloads/

下载完成后，一路next安装好，放着。然后点击academic license申请个证书，如果没账号就注册一个，用qq邮箱比用公司的邮箱会快。公司邮箱会慢点，但是也会收得到，收到验证邮件后点击进去设置密码即可。

1.2 获取学术许可成功

1.3打开gurobi的命令行窗口会提示输入许可

把刚刚那个grbgetkey复制粘贴到这个窗口就完事了

1.4 安装完成

经过以上两步已经完成了gurobi的安装，但是许多同学在安装的最后一步并不会去重启，即使它提示你需要重启。这就会导致环境变量不生效，后面会有意想不到的事情发生。

2.1 Gurobi导入idea中

打开idea，点projecstructure，module。做如下操作

2.2找到gurobi的安装路径的lib目录

添加jar包

添加完成apply，返回开始贴上官方代码。

2.3 运行MIP问题的例子

例子在这，https://www.gurobi.com/documentation/9.1/examples/mip1_java.html，代码如下：

import gurobi.*;

public class Mip1 {
  public static void main(String[] args) {
    try {

      // Create empty environment, set options, and start
      GRBEnv env = new GRBEnv(true);
      env.set("logFile", "mip1.log");
      env.start();

      // Create empty model
      GRBModel model = new GRBModel(env);

      // Create variables
      GRBVar x = model.addVar(0.0, 1.0, 0.0, GRB.BINARY, "x");
      GRBVar y = model.addVar(0.0, 1.0, 0.0, GRB.BINARY, "y");
      GRBVar z = model.addVar(0.0, 1.0, 0.0, GRB.BINARY, "z");

      // Set objective: maximize x + y + 2 z
      GRBLinExpr expr = new GRBLinExpr();
      expr.addTerm(1.0, x); expr.addTerm(1.0, y); expr.addTerm(2.0, z);
      model.setObjective(expr, GRB.MAXIMIZE);

      // Add constraint: x + 2 y + 3 z <= 4
      expr = new GRBLinExpr();
      expr.addTerm(1.0, x); expr.addTerm(2.0, y); expr.addTerm(3.0, z);
      model.addConstr(expr, GRB.LESS_EQUAL, 4.0, "c0");

      // Add constraint: x + y >= 1
      expr = new GRBLinExpr();
      expr.addTerm(1.0, x); expr.addTerm(1.0, y);
      model.addConstr(expr, GRB.GREATER_EQUAL, 1.0, "c1");

      // Optimize model
      model.optimize();

      System.out.println(x.get(GRB.StringAttr.VarName)
                         + " " +x.get(GRB.DoubleAttr.X));
      System.out.println(y.get(GRB.StringAttr.VarName)
                         + " " +y.get(GRB.DoubleAttr.X));
      System.out.println(z.get(GRB.StringAttr.VarName)
                         + " " +z.get(GRB.DoubleAttr.X));

      System.out.println("Obj: " + model.get(GRB.DoubleAttr.ObjVal));

      // Dispose of model and environment
      model.dispose();
      env.dispose();

    } catch (GRBException e) {
      System.out.println("Error code: " + e.getErrorCode() + ". " +
                         e.getMessage());
    }
  }
}

2.4 运行

报错：java.lang.UnsatisfiedLinkError:no gurobi950 in java.library.path
原因是环境变量未生效，重启解决

2.5 运行结果

Set parameter Username
Set parameter LogFile to value "mip1.log"
Academic license - for non-commercial use only - expires 2022-01-09
Gurobi Optimizer version 9.5.0 build v9.5.0rc5 (win64)
Thread count: 4 physical cores, 4 logical processors, using up to 4 threads
Optimize a model with 2 rows, 3 columns and 5 nonzeros
Model fingerprint: 0x98886187
Variable types: 0 continuous, 3 integer (3 binary)
Coefficient statistics:
  Matrix range     [1e+00, 3e+00]
  Objective range  [1e+00, 2e+00]
  Bounds range     [1e+00, 1e+00]
  RHS range        [1e+00, 4e+00]
Found heuristic solution: objective 2.0000000
Presolve removed 2 rows and 3 columns
Presolve time: 0.14s
Presolve: All rows and columns removed

Explored 0 nodes (0 simplex iterations) in 0.22 seconds (0.00 work units)
Thread count was 1 (of 4 available processors)

Solution count 2: 3 2 

Optimal solution found (tolerance 1.00e-04)
Best objective 3.000000000000e+00, best bound 3.000000000000e+00, gap 0.0000%
x 1.0
y 0.0
z 1.0
Obj: 3.0

Process finished with exit code 0