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author | Cathy Yeh <cathy@driver.xyz> | 2017-12-03 19:16:32 -0800 |
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committer | Cathy Yeh <cathy@driver.xyz> | 2017-12-03 20:35:30 -0800 |
commit | 8dc7ae89677fca16ee974a30cff8c4df53c955ce (patch) | |
tree | 6b021dcd7902a2952cc97872f6200469b7dab51b /beliefs/factors/bernoulli_or_cpd.py | |
parent | e5937060658f7e8ac484e5489f2b35b4ecb96d35 (diff) | |
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-rw-r--r-- | beliefs/factors/bernoulli_or_cpd.py | 42 |
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diff --git a/beliefs/factors/bernoulli_or_cpd.py b/beliefs/factors/bernoulli_or_cpd.py new file mode 100644 index 0000000..bfb3a95 --- /dev/null +++ b/beliefs/factors/bernoulli_or_cpd.py @@ -0,0 +1,42 @@ +import numpy as np + +from beliefs.factors.cpd import TabularCPD + + +class BernoulliOrCPD(TabularCPD): + """CPD class for a Bernoulli random variable whose relationship to its + parents (also Bernoulli random variables) is described by OR logic. + + If at least one of the variable's parents is True, then the variable + is True, and False otherwise. + """ + def __init__(self, variable, parents=[]): + """ + Args: + variable: int or string + parents: optional, list of int and/or strings + """ + super().__init__(variable=variable, + variable_card=2, + parents=parents, + parents_card=[2]*len(parents), + values=[]) + self._values = [] + + @property + def values(self): + if not any(self._values): + self._values = self._build_kwise_values_array(len(self.variables)) + self._values = self._values.reshape(self.cardinality) + return self._values + + @staticmethod + def _build_kwise_values_array(k): + # special case a completely independent factor, and + # return the uniform prior + if k == 1: + return np.array([0.5, 0.5]) + + return np.array( + [1.,] + [0.]*(2**(k-1)-1) + [0.,] + [1.]*(2**(k-1)-1) + ) |