Quick question: this tests the case where all the variables are defined by the subtree being transformed. What happens if one of the Vars is defined outside the subtree (e.g., on m instead of under m.b)?

@jsiirola In this example, if we defined variable x as m.x instead of m.b.x, the transformed expression would be:

0.5 * m.x + 3 - m.b.y <= 3.5 * m.b.dis2.binary_indicator_var instead of

0.5 * m.b.x + 3 - m.b.y <= 3.5 * m.b.dis2.binary_indicator_var

Do you see any potential issues with this?

Nope - that should be fine. I don't think it will be a huge issue, as the change this PR is making doesn't actually affect Vars (I wasn't thinking clearly last night -- you are only getting relative names for active components [Constraints & Disjuncts] - and not Vars).

BUT, this does raise the question: what do we expect the following to do??

m.d1 = Disjunct()
m.b = Block()
m.b.d2 = Disjunct()
m.b.disj = Disjunction(expr=[m.d1, m.b.d2])
TransformationFactory('gdp.mbigm').apply_to(m.b, threads=2)

Thoughts? @emma58?

(Spot checking... this update to mbigm leads to an exception. bigm will transform the model (including deactivating m.d1)

(@emma58 crawls under a table...)

(From under the table,) we expect the model above to put the transformed constraints on m.b, and to deactivate m.d1 and m.b.d2. Scoping should be determined by the Disjunction and not care about where the Disjuncts are living at all. So basically, the bigm behavior is the desired behavior. I can look at this...

So actually, the model above transforms without error on this branch (both with m and m.b as the Block being transformed). Even this transforms correctly, as a fun fact:

from pyomo.environ import *
from pyomo.gdp import *

m = ConcreteModel()

m.x = Var(bounds=(0, 10))
m.d1 = Disjunct()
m.b = Block()
m.b.y = Var(bounds=(3, 15))
m.b2 = Block()
m.b2.d2 = Disjunct()
m.b2.d2.c1 = Constraint(expr=m.x <= 7)
m.b2.d2.c2 = Constraint(expr=m.b.y <= 7)

m.b.disj = Disjunction(expr=[m.d1, m.b2.d2])
TransformationFactory('gdp.mbigm').apply_to(m.b, threads=2)

We're somehow getting away with the relative names, though I admit I'm not fully following how at the moment.