Hi all,

I want to propose improvements to the current implementation of Padé 
approximants offered within SciPy. Currently, the method we offer solves a 
toeplitz system which is often highly ill-conditioned. This leads to spurious 
pole-zero pairs or Froissart doublets which means in practice often the 
implementation offered in SciPy is unusable. For example, I am interested in 
Padé approximations to the solution of the Volterra integro-differential 
equations. Here the method in SciPy quickly breaks down.

I would like to propose we replace our current method with a method based on 
the paper by Trefethen et al. [1]. This paper has quite a lot of citations and 
is already implemented in the popular Chebfun package. Hopefully, this part is 
fairly uncontroversial as it is a clear improvement to something we already 
offer. However, there are a couple of questions about adding this:

1. Location.  Currently, our Padé approximation lives within scipy.interpolate. 
Clearly, this is not an interpolation method so this would be a good 
opportunity to think about if there is a better place for this to live.

2. Implement within the old signature or start again. It was suggested that it 
would be easier to start afresh and deprecate the old function. I think this 
would be preferable as we wouldn't be shackled by old design decisions.

As ever, please feel free to join in the discussion either here or on the 
original issue [2].

Regards,
Jake

[1] https://people.maths.ox.ac.uk/trefethen/publication/PDF/2011_144.pdf
[2] https://github.com/scipy/scipy/issues/20064
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