Create multi-dimensional variables, read data file in C++

回答済み

Zeyu Wang

2021年12月20日 16:03

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Hi, 

1. I would like to create several multi-dimensional decision variables in C++ using 

const int I = 3;
const int J = 4;
const int K = 5;
GRBVar* v[I];
for (int i = 0; i < I; i++)
{
v[i] = model.addVars(J, GRB_BINARY);
}

GRBVar* v[I];
for (int i = 0; i < I; i++)
{
for (int j = 0; j < J; j++)
{
v[i] = model.addVars(K, GRB_BINARY);
}
}

May I ask if they are referring to binary variables v[i][j] and v[i][j][k]?

 

2. I need to read coefficients from a data file. I only found examples that define coefficients inside a cpp file, may I ask how to define these constants from a txt or dat file? 

I just switch to C++ from AMPL recently, should I update my data file in a format like 

[1]
[3,3]
[[0.9,0.5],
[0.4,0.8]]
or
1
3,3
0.9,0.5,0.4,0.8

if the coefficients are "b=1, c[1]=3, c[2]=3, d[1,1]=0.9, d[1,2]=0.5, d[2,1]=0.4 and d[2,2]=0.8?

Thank you in advance!

0

• 正式なコメント

  

  Simranjit Kaur

  • Gurobi Staff

  2025年06月23日 02:42 編集済み

  This post is more than three years old. Some information may not be up to date. For current information, please check the Gurobi Documentation or Knowledge Base. If you need more help, please create a new post in the community forum. Or why not try our AI Gurobot?.
• 

  Jaromił Najman

  • Gurobi Staff

  2021年12月21日 09:10 編集済み

  Hi,

  Regarding your first question. The workforce1_c++.cpp example shows an application of a 2 dimensional variable object. For 3 dimensions, your code might look something like

  #include "gurobi_c++.h"
  #include <sstream>
  using namespace std;
  
  [...]
  
  int I = 3;
  int J = 4;
  int K = 5;
  GRBVar*** vars = 0;
  [...]
  vars = new GRBVar**[I];
  for(int i = 0; i < I; i++){
    vars[i] = new GRBVar*[J];
    for(int j = 0; j < J; j++){
      vars[i][j] = model.addVars(K);
      for(int k = 0; k < K; k++){
        ostringstream vname;
        vname << "v[" << i << "," << j << "," << k << "]";
        vars[i][j][k].set(GRB_CharAttr_VType, GRB_BINARY);
        vars[i][j][k].set(GRB_StringAttr_VarName, vname.str());
      }
    }
  } 
  for (int i = 0; i < I; i++){
    GRBLinExpr lhs = 0;
    for (int j = 0; j < J; j++){
      for(int k = 0; k < K; k++){
        lhs += vars[i][j][k];
      }
    }
    model.addConstr(lhs == 1);
  }
  [...]
  
  // Don't forget to delete
  for (int i = 0; i < I; i++){
    for (int j = 0; j < J; j++){
      delete[] vars[i][j];
    }
    delete[] vars[i];
  }
  delete[] vars;

  Regarding your second question. There is a vast number of ways to read in data from a file in C++. One way is described in the stackoverflow post Read file line by line using ifstream in C++.
  
  Best regards,
  Jaromił

  0
• 

  Zeyu Wang

  2021年12月21日 15:26 編集済み

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  Thank you so much for your help Jaromił! That helps me a lot! 

  Best,

  Zeyu

  0

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