Suggestion: Add diff and zero-crossing rate algoritms for math

[perdo-nober-rs]

Hello I work as audio engineer and often do audio process. I am interested in learning the Rust and would like to see some signal process algorithm. I see you already have fft, so maybe some simpler algo wouldn't hert. First off I'd suggest adding the "diff" of a vector, or y[n] = x[n] - x[n-1] in signal discrete time. As matlab documentation say:

If X is a vector of length m, then Y = diff(X) returns a vector of length m-1. The elements of Y are the differences between adjacent elements of X.

Y = [X(2)-X(1) X(3)-X(2) ... X(m)-X(m-1)]

Also I would like zero cross rate to be added too, This function shows a signal's tendency of changing sign, sort of like a derivative show rate of change. zero cross rate of vector to vector is implemented as Y = diff(sgn(x)) or similar. Thank for your attention.

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