3 files changed, 40 insertions, 0 deletions
diff --git a/beliefs/utils/__init__.py b/beliefs/utils/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/beliefs/utils/__init__.py
diff --git a/beliefs/utils/math_helper.py b/beliefs/utils/math_helper.py
new file mode 100644
index 0000000..a25ea68
--- /dev/null
+++ b/beliefs/utils/math_helper.py
@@ -0,0 +1,19 @@
+"""Random math utils."""
+
+
+def is_kronecker_delta(vector):
+    """Returns True if vector is a kronecker delta vector, False otherwise.
+    Specific evidence ('YES' or 'NO') is a kronecker delta vector, whereas
+    virtual evidence ('MAYBE') is not.
+    """
+    count = 0
+    for x in vector:
+        if x == 1:
+            count += 1
+        elif x != 0:
+            return False
+
+    if count == 1:
+        return True
+    else:
+        return False
diff --git a/beliefs/utils/random_variables.py b/beliefs/utils/random_variables.py
new file mode 100644
index 0000000..1a0b0f7
--- /dev/null
+++ b/beliefs/utils/random_variables.py
@@ -0,0 +1,21 @@
+
+
+def get_reachable_observed_variables_for_inferred_variables(model, observed=set()):
+    """
+    After performing inference on a BayesianModel, get the labels of observed variables
+    ("reachable observed variables") that influenced the beliefs of variables inferred
+    to be in a definite state.
+
+    INPUT
+      model: instance of BayesianModel class or subclass
+      observed: set of labels (strings) corresponding to vars pinned to definite
+        state during inference.
+    RETURNS
+      dict, of form key - source label (a string), value - a list of strings
+    """
+    if not observed:
+        return {}
+
+    source_vars = model.get_unobserved_variables_in_definite_state(observed)
+
+    return {var: model.reachable_observed_variables(var, observed) for var in source_vars}