How to access the RV corresponding to a mixture component?

Questions
1

Hi,

When building a mixture, like the small example below, I noticed that the RV corresponding to the mixture are not accessible…!
The RV c1 & c2 are not in the trace output.
Calling trace['c1'] yield an error, same for c2.

I don’t understand why we can’t access them.

import numpy as np
import pymc3 as pm

data = np.random.normal(size=100)

with pm.Model() as model:
    c1 = pm.Normal.dist(mu=0,sd=1)
    c2 = pm.Normal.dist(mu=1,sd=1)
    w = pm.Dirichlet('w',a=np.array([1,1]))
    mix = pm.Mixture('mix',comp_dists=[c1,c2],w=w, observed=data)
    trace = pm.sample()

This problem is getting even worse when I discovered that it’s not even accessible during the samping. I wanted to add a penalty to the c1 parameter using a Potential, with the following code :

import numpy as np
import pymc3 as pm

data = np.random.normal(size=100)

with pm.Model() as model:
    c1 = pm.Normal.dist(mu=0,sd=1)
    c2 = pm.Normal.dist(mu=1,sd=1)
    p= pm.Potential('p',c1*c1) # added potential
    w = pm.Dirichlet('w',a=np.array([1,1]))
    mix = pm.Mixture('mix',comp_dists=[c1,c2],w=w, observed=data)
    trace = pm.sample()

outputs this error message :

TypeError: unsupported operand type(s) for *: ‘Normal’ and ‘Normal’

(Note : The value used in the potential is a dummy one, it’s just to show that you can’t access c1 or c2 during sampling.)

I’d appreciate any help or link to documentation to better understand what happen here…