This question is a duplicate of this question on StackOverflow, but it hasn't been answered in 2 years, which is why I'm re-posting it. If this isn't an appropriate way to go about this, please let me know as I'm new to the community.
The piecewise-linear activation function as defined in Neural Networks by Simon S. Haykin has three pieces, one of which is:
$φ(v) = v, -0.5 < v < 0.5$
Haykin presents this graph of the function:
in which $φ(v)$ increases linearly w.r.t. $v$ in the region $-0.5<v<0.5$.
As far as I can tell, this graph doesn't describe the function above. For example, for $v = 0$, $φ(v) = 0.5$ instead of $0$. In fact, it seems that the actual definition of $φ(v)$ in that region is $φ(v) = v + 0.5$.
This mistake seems so obvious that I must be missing something.