adding typos

doc/src/How2ReadData/How2ReadData.do.txt

@@ -942,10 +942,10 @@ It is less sensitive to outliers in data than the squared error cost function.
 A variant for classification is also sometimes used, a quantity we will meet later. 
 !bt
 \[
-L_{\delta }(a)={\begin{cases}{\frac {1}{2}}{a^{2}}&{\text{for }}|a|\leq \delta ,\\\delta (|a|-{\frac {1}{2}}\delta ),&{\text{otherwise.}}\end{cases}}}.
+H_{\delta}(a)={\begin{cases}{\frac {1}{2}}{a^{2}}&{\text{for }}|a|\leq \delta ,\\\delta (|a|-{\frac {1}{2}}\delta ),&{\text{otherwise.}}\end{cases}}}.
 \]
 !et
-
+Here $a=\bm{y} - \bm{\tilde{y}}$.
 We will discuss in more
 detail these and other functions in the various lectures.  We conclude this part with another example. Instead of 
 a linear $x$-dependence we study now a cubic polynomial and use the polynomial regression analysis tools of scikit-learn.