mdmultispec silently modifies input

[Andy Nowacki]

mdmultispec modifies the input vector x in place without declaring this in the docs:

julia> using Multitaper

julia> x = collect(1:10)
       y = rand(10)
       y′ = copy(y)
       mdmultispec(x, y′)
       y == y′
false

This is because x is modified in place in multispec_coef at src/MDmwps.jl:48:

function multispec_coef(tt, x, u, n, nfft, nfft2)
  x     .-= mean(x)

Two possible solutions:

1. Modify multispec_coef so that x̂ = x .- mean(x), and using the new vector `x̂` which has the mean removed. (Preferred option probably.)
2. Change the name of multispec_coef to multispec_coef!, document that the x argument is updated, and do likewise for mdmultispec → mdmultispec!

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[Charlotte Haley]

I’m glad you caught this. I’ve followed your first suggestion here.

[Andy Nowacki]

This is great, thanks.

Usually when bugs are found, I would also add a test to check things work as per the fix. I’m not sure that is so strictly needed here, though, and I’m happy with this fix.

[Charlotte Haley]

Thanks, will test in the future.