Gurobi Python code to print non-binding constraints?

Answered

Tanmoy Das

February 10, 2023 01:08

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Hello good people,

How can I correctly write/save the model.lp file to store non-binding constraints as well?

When I write the model.lp file, most constraints are found formulated as expected. However, LHS of non-binding constraint (constraints that do not contain any decision variables) is empty in the .lp file. 

part of model.lp file
 C_available_resources[m,s16]: deploy[s16,o186,m] + deploy[s16,o217,m]  <= 300
 C_available_resources[c,s16]: deploy[s16,o186,c] + deploy[s16,o217,c]<= 10
 C_available_resources[i,s16]: deploy[s16,o186,i] + deploy[s16,o217,i]<= 30
 C_max_distance[s2,o186]: <= 0
 C_max_distance[s2,o217]: <= 0
 C_max_distance[s18,o186]: <= -1

 

# a binding constraint (deploy[] is a decision variable
C_available_resources = model2.addConstrs((gp.quicksum(deploy[s, o, r] for o in OilSpills)
                                           <= Availability[s, r] for s in Stations for r in ResourcesD),
                                          name='C_available_resources')
# a non-binding constraint
C_max_distance = model2.addConstrs((Distance[s, o] <= DistanceMax for s in Stations for o in OilSpills),
                                   name='C_max_distance')

 

Related to

• Model Files
• Python

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  Riley Clement

  • Gurobi Staff

  February 10, 2023 01:26

  Hi Tanmoy,
  
  If there are no Gurobi variables in your expression, then it is not really a constraint (nothing is being constrained).
  
  Are you perhaps just wanting to calculate the maximum of the numbers stored in the Distance dictionary?  If so you can define DistanceMax like so

  DistanceMax = max(Distance.values())

  and then use it in your model.
  
  
  - Riley

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  Tanmoy Das

  February 10, 2023 01:37

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  Well, actually Distance[s, o] is more of a Pairing of index between s & o. Just like Pairing(i,j) example in the following example https://gurobi.github.io/modeling-examples/customer_assignment/customer_assignment.html

  But, I want to use it as constraint so that this constraint would be violates sometimes based on certain conditions. So, I used all values as pair index.  

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  Riley Clement

  • Gurobi Staff

  February 10, 2023 01:46

  Hi Tanmoy,

  If you want a list of pairings (s,o) where Distance[s,o] is less than DistanceMax then you can create this like so

  [index for index,distance in Distance.items() if distance <= DistanceMax]

  - Riley

  0

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