values clobbering new substitutions because of constraint ordering choice

[mjburton11]

Looking at commit convexengineering/solar@e99e9e7 in solar, solving solar.py and convexengineering/gplibrary@c6da5c0 in gpkitmodels. I am subbing in tau in HTail.

class HorizontalTail(AeroSurf):
    "horizontal tail model"
    flight_model = TailAero
    sparModel = None

    def setup(self, N=3, lam=0.8):
        self.ascs = AeroSurf.setup(self, N, lam)
        self.planform.substitutions.update({"AR": 4, "\\tau": 0.08})

But when I solve the model I get this:

In [2]: sol("\\tau")
Out[2]: 
{\tau_Mission/Aircraft/Empennage/HorizontalTail/Planform: 0.115,
 \tau_Mission/Aircraft/Empennage/VerticalTail/Planform.1: 0.115,
 \tau_Mission/Aircraft/AeroSurf/Planform.2: 0.115}

In [3]: M.substitutions["\\tau_Mission/Aircraft/Empennage/VerticalTail/Planform.
   ...: 1"]
Out[3]: 0.115

In [4]: sol("AR")
Out[4]: 
{AR_Mission/Aircraft/Empennage/HorizontalTail/Planform: 4,
 AR_Mission/Aircraft/Empennage/VerticalTail/Planform.1: 3.7197870897370509,
 AR_Mission/Aircraft/AeroSurf/Planform.2: 26.66897625889953}

Pretty weird that AR got changed, but not tau

[bqpd]

the problem is in

https://github.com/convexengineering/solar/blob/e0d1f51459d945b3c71ff23012c9001c358168bf/solar/solar.py#L320

because self.mission contains \\tau (in the performance models), but no substitutions for it, it pulls the value out of the variable. Because it comes second in the list, its substitutions replace those of self.solar

In the short term this can be fixed by reordering them: return self.mission, self.solar

In the medium term this requires a different approach to substitutions

[mjburton11]

Interesting. The reordering worked. Feels like this shouldn't be a problem. Maybe a design discussion question??