Retrieve a specific subset value of variables

Answered

Sander Mertens

January 31, 2023 15:56

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Hello,

Is there a way to retrieve the value of a subset from a specific variable within Gurobi?

For instance, allot of X variables are created in the form of X[a,b,c,t]. After optimization, I want to retrieve for a variable with a specific a,b,c combination (lets say 'X[1,0,0'), the largest value of t of all the instances where this X[1,0,0,t] = 1. 

Related to

• Python

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  Riley Clement

  • Gurobi Staff

  January 31, 2023 22:30 Edited

  Hi Sander,
  
  There are several ways you could do this in python (or our interactive interface).  Here is one approach:

  ind = (1,0,0)  # the a,b,c values you want to match
  eps = 1e-6  # tolerance to use for comparison in case values are not exactly 1

  largest_t = sorted([t for (a,b,c,t),v in X.items() if (a,b,c) == ind and abs(v.X - 1) < eps])[-1]

  In this approach we loop through the X dictionary (whose values are variables) with a list comprehension, finding those t values for which the a,b,c indices match and whose variable value is 1 (or close enough to 1).  The list of t values is then sorted from smallest to largest and we take the last one using the -1 index.
  
  Note this approach will result in a list index out of range error if there are no t values which satisfy the condition.

  - Riley

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  Sander Mertens

  February 01, 2023 08:48

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  Thank you, works perfect!

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