Create a array of binaries variables should I use Gurobi C++

Answered

November 28, 2020 16:25 Edited

Hi,

I am using Gurobi C++, and I m trying to introduce binaries variables as elements of a vector to 1 the machine is on,0 otherwise. How could I do it? Also is it possible to create a vector of Gurobi QuadExpr to manage time 0 to T lines equal to predefined value ?

Should I avoid use Gurobi C++ for large size constrained problem?

Thanks in advance for any help.

BR,

Alessandra

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6 comments

Official comment
Simranjit Kaur

Gurobi Staff

December 06, 2024 00:49
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?.
Matthias Miltenberger

Gurobi Staff

November 30, 2020 15:58
Hi Alessandra,

It's perfectly fine to use our C++ API to construct your model. Why would you think otherwise? We just recommend using Python for its usability.

Please refer to our documentation on addVars() and our numerous C++ examples to get an idea of how to implement this.

Cheers,
Matthias
0
Alessandra Vieira

December 07, 2020 16:50
Hi Matthias,

I want to get a sum of two variables multiplied over many elements in a loop, it seems that I am just getting one single element of this multiplication.
```
GRBVar P_[T][N_GEN] ;   // (integer, LB, UP)
GRBVar w_t_i[T][N_GEN];  // ( binary, Lb_0,UP_1)
GRBQuadExpr expr[t]={0};

for (t=0,t<T,t++){
  for(gen=0,gen<N_GEN,gen++){
    expr[t] +=P_[t][gen]*w_t_i{t][gen];
  }
}
```
It seems the syntax is correct for C++ but not for Gurobi because it just one single element but not the sum. What I am doing wrong ? The result is zero when it should be >0 , as all w_t_i are 1 , and the P_ > 0 . When I add the constraint then my model becomes infeasible.

Any help?

Thanks
Alessandra.
0
Matthias Miltenberger

Gurobi Staff

January 07, 2021 15:33
Hi Alessandra,

Please excuse me for not coming back to you earlier. Have you already been able to make your code work in the meantime?

Something's definitely off with your indices. You are using "t" to declare the "GRBQaudExpr expr" instead of "T". Do you intend to add all terms to a single expression?

Cheers,
Matthias
0

Alessandra Vieira

January 08, 2021 10:16

Hi Matthias,

Thanks for your answer!

What I want now is that the expression that will be minimized besides the coefficient ( C_), also be multiplied for two variables Gurobi, integer P_, and other binary w_t_i. I expect that way that the model has both the Gurobi variable as part of the decision in the optimization process. The OBJ function is to minimize the sum of little expressions the same as :

//the expression takes the value of variables for many members at time t, to minimize the cost per hour
for (int t = 0; t < T; t++) {
  for (int i = 0; i < N_GEN; i++) {
    exprObj1 += C_[i] * P_[t][i]*w_t_i[t][i];
    for (int bess = 0; i < N_BESS; bess++) {
      exprObj2 += Cssd_[bess]*P_discharge[t][bess]*ssd_[t][bess];
    }
  }
}

I got these messages, and failed to build my object file!

> error C2679: binary '+=': no operator found which takes a right-hand operand of type 'GRBQuadExpr' (or there is no acceptable conversion)
1>could be 'void GRBLinExpr::operator +=(const GRBLinExpr &)'
1>\HolisticSolver_rm.cpp(487,53): message: while trying to match the argument list '(GRBLinExpr, GRBQuadExpr)'

I tried already the overloaded operator as examples in Gurobi documentation, but it does not work.

Any help I will very happy!

Matthias Miltenberger

Gurobi Staff

January 08, 2021 12:13
Hey Alessandra,

It looks like you are trying to add a quadratic expression to a LinExpr object. Please make sure, that both exprObj1 and exprObj2 are of type QuadExpr.

You may also try using addTerms() as suggested in the documentation about quadratic expressions.

Cheers,
Matthias
0

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Create a array of binaries variables should I use Gurobi C++

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