update week 45

doc/src/week45/week45.do.txt

@@ -412,7 +412,7 @@ observations of this class in the region $R_m$ as
 
 !bt
 \[
-p_{mk} = \frac{1}{N_m}\sum_{x_i\in R_m}I(y_i=k).
+p_{mk} = \frac{1}{N_m}\sum_{i\in R_m}I(y_i=k).
 \]
 !et 
 
@@ -422,7 +422,7 @@ $m$. The three most common ways of splitting a node are given by
 * Misclassification error 
 !bt
 \[
-p_{mk} = \frac{1}{N_m}\sum_{x_i\in R_m}I(y_i\ne k) = 1-p_{mk}.
+\frac{1}{N_m}\sum_{i\in R_m}I(y_i\ne k) = 1-p_{mk}.
 \]
 !et 
 * Gini index $g$