Editing docstring for Label Model (#1468)

* Editing docstring

* Resolving PR edits

Author: ajratner

snorkel/labeling/model/label_model.py

@@ -87,7 +87,22 @@ class _CliqueData(NamedTuple):
 
 
 class LabelModel(nn.Module):
-    """A conditionally independent LabelModel to learn LF weights and assign training labels.
+    r"""A model for learning the LF accuracies and combining their output labels.
+
+    This class learns a model of the labeling functions' conditional probabilities
+    of outputting the true (unobserved) label `Y`, `P(\lf | Y)`, and uses this learned
+    model to re-weight and combine their output labels.
+
+    This class is based on the approach in [Training Complex Models with Multi-Task
+    Weak Supervision](https://arxiv.org/abs/1810.02840), published in AAAI'19. In this
+    approach, we compute the inverse generalized covariance matrix of the junction tree
+    of a given LF dependency graph, and perform a matrix completion-style approach with
+    respect to these empirical statistics. The result is an estimate of the conditional
+    LF probabilities, `P(\lf | Y)`, which are then set as the parameters of the label
+    model used to re-weight and combine the labels output by the LFs.
+
+    Currently this class uses a conditionally independent label model, in which the LFs
+    are assumed to be conditionally independent given `Y`.
 
     Examples
     --------