CODEWITHSUNDEEP
pythonpython-2.7pymc
Shobhit
Shobhit

Reputation: 767

PYMC Deterministic variable with parent as class attribute

I am trying to create a PYMC Deterministic variable that looks like the following.

@pymc.deterministic
def tau(s = sigma):
    return 1.0/(s**2)

However, in my case, the model parameters (PYMC Stochastic variables) are defined as class attributes. As a result, sigma is accessible only to class methods (through self.sigma). Trying to make this a class method like the following

@pymc.deterministic
def tau(self, s = None):
    sigma = self.sigma
    return 1.0/(sigma**2)

throws an error (obviously).

ValueError: Deterministic tau: no parent provided for the following label: self

How can I create a PYMC Deterministic variable whose parent is an attribute of a class?

P.S. Not sure if it matters, but I am using PYMC 2.x

Upvotes: 0

Views: 385

Answers (1)

Shobhit
Shobhit

Reputation: 767

Thanks to this mildly related question, I was able to figure out a way to capture class attributes as parents to a PYMC Deterministic variable. The solution is to use PYMC's Lambda class which converts a Python lambda function into a Deterministic instance. This seems to be a rather clean way.

self.tau = pymc.Lambda('tau', lambda s = self.sigma: 1.0/(s**2))

Upvotes: 1

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