For example, the non-differentiable point of the function $f(x)=|x|$ is at $x=0$.
How to find the non-differentiable points of a continuous function that is defined numerically?
If we define
the following returns interesting points:
Let's try another function defined with
then we needn't use
One should be careful when working with
Here is an approach that you can use for numerical functions that at least have a left and right derivative. If such a function isn't differentiable in a point that is equivalent to the left and right derivatives being unequal, so look at the left and right finite difference approximation of the derivative, and see where they disagree.
Using this you can use some numerical maximization on