update

doc/src/week36/week36.do.txt

@@ -531,7 +531,7 @@ which gives $\lambda=4.571$ and $\beta_0=0.933$ and $\beta_1=0.359$.
 ===== Lasso case =====
 
 For Lasso we need now, keeping a  constraint on $\vert\beta_0\vert+\vert\beta_1\vert=1$,  to take the derivative of the absolute values of $\beta_0$
-and $beta_1$. This gives us the following derivatives of the cost function
+and $\beta_1$. This gives us the following derivatives of the cost function
 !bt
 \[
 C(\bm{\beta})=(4-2\beta_0)^2+(2-\beta_1)^2+\lambda(\vert\beta_0\vert+\vert\beta_1\vert),
@@ -856,7 +856,7 @@ Taking the derivative of the *new* cost function with respect to the parameters
 which leads to
 !bt
 \[
-\hat{\bm{\beta}}_{mathrm{OLS}}=\left(\bm{X}^T\bm{X}\right^{-1}\bm{X}^T\bm{y}!
+\hat{\bm{\beta}}_{\mathrm{OLS}}=\left(\bm{X}^T\bm{X}\right)^{-1}\bm{X}^T\bm{y}!
 \]
 !et