Combined AP & Window Convolution with Chebyshev polynomials

[marcobonici]

The convolution with a Window mask requires the multiplication with a matrix with ~ 1000 k bins. This means that we have to resample our mutlipoles on a very expensive grid (especially when we consider the cost of backward AD!).

The idea is to resample the multipoles on a Chebyshev grid, then using the Chebyshev coefficients to compute the convolution.