Using a tuple as first part of a double indeces

Answered

Markus Gabl

January 17, 2020 15:10

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Hi 

I have a tuplelist 

arcs = [(1,2),(3,4)]

and a list

uncer = [1,2]

and I create a variable with a double index 

v = model.addVars(arcs, uncer, vtype=GRB.BINARY, name="v")

Now the indeces of the variables are not 

((1,2),1),((1,2),2), ((3,4),1), ((3,4),2)

but 

(1,2,1),(1,2,2), (3,4,1), (3,4,2)

so addVars turned a tuple and a number into a triple. 

This clashes with :

quicksum(v[a,k] for a in arcs for k in uncer)

since it looks for variables with indeces of the form ((1,2),1),ect... but they of course do not exist. 

Is there an easy solution where I can keep uncer and arcs as they are (I need them in other places) ? 
Preferably, there should be a way to tell gurobi that the first index of the variable 'v' is a tuple. 

Many thanks in advance 
Markus 

 

 

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• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  June 23, 2025 03:19 Edited

  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?.
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  Silke Horn

  • Gurobi Staff

  January 17, 2020 16:49

  The result of model.addVars is tupledict, whose keys are of type tuplelist and can only store tuples of scalar values.

  One way to do your quicksum would be:

  quicksum(v[a[0],a[1],k] for a in arcs for k in uncer)

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  Markus Gabl

  January 17, 2020 16:56

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  Thanks a lot for you quick answer! That is a very helpful and simple solution. 

  Have a nice weekend :) 

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