In the context of neural networks and cryptography, I would like to approximate some activation functions. However, I need to approximate them into polynomial forms for my purpose.
It seems that chebyshev polynomial approximation is the more suited one for my case, but while I read in some papers that we can enlarge the approximation for a bigger interval, all the algorithms i've seen throughout the web only mention the case $[-1,1]$...
So how do we compute this process to get a polynomial approximation of a function given an interval $[a,b]$ (the interval can be considered as $[-a,a]$ if it is easier)
If some of you have a clue to this, I would be very grateful! Thank you