How to properly write a constraint with the right hand side needs to choose among three possible numbers

Answered

Sabrin Rashwan

July 04, 2020 16:45 Edited

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I have a constraint with the right-hand side that needs to choose among three possible numbers. Regardless the left handside, my focus now is on the right-hand side. The constraint is shown in the next image. I set the f parameter as follows

f = 1 if i in P else -1 if i in D else 0

Note: Cr contains P and D

By the way, this is my trial for the left- hand side.

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• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  June 23, 2025 03:10 Edited

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  Eli Towle

  • Gurobi Staff

  July 06, 2020 19:53 Edited

  Hi Sabrin,

  Since \( f_i^r \) is indexed by both \( i \) and \( r \), you will need something like a dictionary or a function that maps the different values of \( i \) and \( r \) to their respective \( f \) values. E.g.:

  f = {(r, i) : 1 if i in P else -1 if i in D else 0 for r in R for i in Cr[r]}

  Then, you can use \( \texttt{f[r, i]} \) on the right-hand sides of the constraints.

  I see that \( y_{ij}^r \) is dependent on \( r \) in your mathematical formulation. However, in your code, you use \( \texttt{yr[i, j]} \), which has no dependency on \( \texttt{r} \). Is there a reason why the \( \texttt{y} \) variables in your code have no dependency on \( \texttt{r} \)?

  Thanks,

  Eli

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  Sabrin Rashwan

  August 06, 2020 13:52

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  Thanks a lot I was searching for something like that. 

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  Sabrin Rashwan

  August 06, 2020 13:57

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  With regard to the yr[i,j] I have corrected to yr[r,i,j]

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