DOC Fix math notation error in description of CCP
Breiman, Friedman, Ohlsen, Stone use a T with a tilde to denote the terminal nodes of a tree. A simple T would imply we are counting the nodes in the whole tree.
@@ -536,9 +536,9 @@ a given tree :math:`T`:
.. math::
- R_\alpha(T) = R(T) + \alpha|T|
+ R_\alpha(T) = R(T) + \alpha|\widetilde{T}|
-where :math:`|T|` is the number of terminal nodes in :math:`T` and :math:`R(T)`
+where :math:`|\widetilde{T}|` is the number of terminal nodes in :math:`T` and :math:`R(T)`
is traditionally defined as the total misclassification rate of the terminal
nodes. Alternatively, scikit-learn uses the total sample weighted impurity of
the terminal nodes for :math:`R(T)`. As shown above, the impurity of a node
