gams constraint to pyomo

[Niki T.]

Hello,

I am new to pyomo and I have a question regarding sets.

I have a set t in gams and its alias tt

Set t / t1*t30 /;

alias (t,tt);

and the following constraint

MSBnew(p,m,t)..DURV(p,m,t)=e=sum(tt$(ord(tt)<=ord(t)), INM(p,m,tt-1)-OUTM(p,m,tt))+OUTM(p,m,t); 

In pyomo i translated it as:

model.t = Set() 

model.tt = Set(initialize=model.t) 

def MSBnew_rule(model,p,m,t):

    return model.DURV[p,m,t] == sum(model.INM[p,m,tt-1]-model.OUTM[p,m,tt] for tt in model.tt if tt<=t) + model.OUTM[p,m,t] 

model.MSBnew = Constraint(model.p, model.m, model.t, rule=MSBnew_rule)

But I get the error :

TypeError: unsupported operand type(s) for -: 'str' and 'int'

Could you please help me formulate this gams constraint in pyomo?

[Siirola, John D]

The problem is you are using string values in your Set (which is perfectly fine and something that Pyomo supports).  However, when you iterate over the Set, you are getting strings, so you cannot directly “do math” on the set values.  Instead, you should make use of the Set’s `ord()`, `next()`, and `prev()` methods.

 

I would do something similar to:

 

model.t = Set() # note that since Pyomo 5.6, Pyomo sets are ordered by insertion order unless otherwise specified

 

def MSBnew_rule(model, p, m, t):

    return model.DURV[p, m, t] == sum(

        model.INM[p, m, model.t.prev(tt)] - model.OUTM[p, m, tt]

        for tt in model.t if model.t.ord(tt) <= model.t.ord(t)

    ) + model.OUTM[p, m, t] 

model.MSBnew = Constraint(model.p, model.m, model.t, rule=MSBnew_rule)

 

John

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[Niki T.]

That is so helpful. Thank you very much!