1 files changed, 42 insertions, 0 deletions
diff --git a/beliefs/factors/BernoulliOrFactor.py b/beliefs/factors/BernoulliOrFactor.py
new file mode 100644
index 0000000..4f973ae
--- /dev/null
+++ b/beliefs/factors/BernoulliOrFactor.py
@@ -0,0 +1,42 @@
+import numpy as np
+
+
+class BernoulliOrFactor:
+    """CPD class for a Bernoulli random variable whose relationship to its
+    parents is described by OR logic.
+
+    If at least one of a child's parents is True, then the child is True, and
+    False otherwise."""
+    def __init__(self, child, parents=set()):
+        self.child = child
+        self.parents = set(parents)
+        self.variables = set([child] + list(parents))
+        self.cardinality = [2]*len(self.variables)
+        self._values = None
+
+    @property
+    def values(self):
+        if self._values is None:
+            self._values = self._build_kwise_values_array(len(self.variables))
+            self._values = self._values.reshape(self.cardinality)
+        return self._values
+
+    def get_values(self):
+        """
+        Returns the tabular cpd form of the values.
+        """
+        if len(self.cardinality) == 1:
+            return self.values.reshape(1, np.prod(self.cardinality))
+        else:
+            return self.values.reshape(self.cardinality[0], np.prod(self.cardinality[1:]))
+
+    @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)
+        )