Generate parameters in Abstract Model in Pyomo

[MUHAMMAD WAQAS SWATI]

I am using Networkx to define a graph G and later use it in my abstract model of pyomo.

The graph contains few nodes. I want to create pyomo abstract constraints equal to the number of nodes in graph. The graph G is:

def mygraph():
    G = nx.Graph() #Some nodes are defined here

Later, I am using my graph in my Pyomo Abstract Model as:

def mymodel(): #Abstract Model Creation
     model = AbstractModel()
     g=mygraph() #Graph passed to pyomo function

 

I want to create constraints for each node of the graph and pprint() it to verify. Like, suppose my graph has 6 nodes then there must be 6 constraints. I am trying to do so as:

    model.nodes_range = RangeSet(1, len(g)) # this creates a parameter with same size of the graph

    model.C = Param(model.nodes_range, within=NonNegativeIntegers) # one parameter for each node

    model.D = Param(model.nodes_range, within=NonNegativeIntegers)

    def const1(model):# Dummy constraint
           return sum(model.C[u] for u in model.nodes_range)<=model.D[u]

    model.constraint1=Constraint(model.nodes_range, rule=const1)

    model.constraint1.pprint()

mymodel()

However, I am not getting constraints with this for each node. Can you guide me with this?
Kind Regards

[David Woodruff]

These days, most people are creating a ConcreteModel so you might be happier doing that.

But either way, I am surprised you don't get an error message because

  model.constraint1=Constraint(model.nodes_range, rule=const1)

implies that const1 will take two arguments: the model and a node.

Dave

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[MUHAMMAD WAQAS SWATI]

Dave, thank you. You've always been extremely helpful. Instead of doing things hard-coded in Concrete Model, I'm using Abstract Model so that I can read different graphs and optimize them.
Could you please explain my coding error? I didn't understand what you were saying.

[David Woodruff]

If you, or your library, can obtain a copy of the third edition of the Pyomo book, it will show you how to do what you want to do using a ConcreteModel:

ISBN: 3030689301

ISBN13: 9783030689308

To quickly answer your question:

Constraint(model.nodes_range, rule=const1)

tells Pyomo to call the function const1 once for each member of model.nodes_range and pass that in as an argument (for the first function argument is always the model). This is explained much better in the book.

  Dave

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