Variable with different indices

回答済み

Tim

2023年10月23日 09:36

• 
• 

Hi everyone,

I try to model an optimization problem where I have a variable with changing indices.

I am ignoring the randomness in the objective function in the first place. 

In the objective function, p is summed over c while in the first constraint the index is just f and I have to make this constraint valid for all f. So is there a way to model the variable with two indices but just using the one needed in the respective equation?

Many thanks

Tim

0

• 正式なコメント

  

  Simranjit Kaur

  • Gurobi Staff

  2026年11月13日 01:36

  This post is more than two 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 try Gurobot, our chatbot interface offering instant, expert-level support.
• 

  Eli Towle

  • Gurobi Staff

  2023年10月23日 18:24 編集済み

  It looks to me like the indexing of \( p \) in the objective function is consistent with the indexing of \( p \) in the constraints. Namely, in the objective function, \( p \) is indexed by a single element of \( F \). However, that single index is \(\bar{f}_{r,c}\), meaning different combinations of \( c \in C \) and \( r \in R\) could correspond to different elements of \( F \).

  To translate this into code, you would need to define the dictionary \( \bar{f} \) that maps \( r \in R \) and \( c \in C \) to an element of \( F \). As long as your \( p \) variables are indexed by \( F \), you can then index \( p \) by \( \bar{f}_{r,c} \in F\). Below is a short Python script that shows one way to approach this.

  import gurobipy as gp
  
  R = [0, 1, 2, 3, 4]
  C = [0, 1, 2]
  
  # F = [0, ..., 14]
  F = list(range(len(R) * len(C)))
  print(f"F = {F}")
  
  # fbar maps each (r, c) pair an index of F
  fbar = {(r, c): len(C) * r + c for r in R for c in C}
  print(f"fbar = {fbar}")
  
  m = gp.Model()
  
  # Create p variables, indexed by F
  p = m.addVars(F, name="p")
  m.update()
  print(f"p = {p}")
  
  for r in R:
      for c in C:
          print(
              f"r={r}, c={c}: fbar[r,c]={fbar[r,c]}, p[fbar[r,c]] = {p[fbar[r,c]]}"
          )

   

  0

投稿コメントは受け付けていません。