update

doc/src/week35/exercisesweek35.do.txt

@@ -13,11 +13,12 @@ derivatives as well as when we analyze various properties (like second
 derivatives) of the chosen cost functions.  Vectors are always written
 as boldfaced lower case letters and matrices as upper case boldfaced
 letters. You will find useful the notes from week 35 on derivatives of vectors and matrices.
+See also the textbook of Faisal at al, chapter 5 and in particular sections 5.3-5.5 at URL:"https://github.com/CompPhysics/MachineLearning/blob/master/doc/Textbooks/MathMLbook.pdf"
 
 Show that
 !bt
 \[
-\frac{\partial (\bm{b}^T\bm{a})}{\partial \bm{a}} = \bm{b},
+\frac{\partial (\bm{a}^T\bm{x})}{\partial \bm{x}} = \bm{a}^T,
 \]
 !et
 and
@@ -37,7 +38,8 @@ and finally find the second derivative of this function with respect to the vect
 The second derivative of the mean squared error is then proportional to the so-called Hessian matrix $\bm{H}=\bm{X}^T\bm{X}$.
 
 
-_Hint_: In these exercises it is always useful to write out with summation indices the various quantities.
+_Hint_: In these exercises it is always useful to write out with summation indices the various quantities. Take also a look at the weekly slides from week 35 and the various examples included there.
+
 As an example, consider the function
 
 !bt