Five argument mul!

[ranocha]

I couldn't find a 5 argument method of mul! in FFTW.jl for FFTW.rFFTWPlan and its siblings. Would it be reasonable to add such methods? In particular, I would like to be able to do something like

julia> using LinearAlgebra, FFTW

julia> x = Vector(range(0., 1., length=16));

julia> rfft_plan = plan_rfft(x);

julia> y = rfft_plan * x; y .= 1;

julia> mul!(y, rfft_plan, x);

julia> mul!(y, rfft_plan, x, 1.0, 0.5) # this yields a MethodError

Note: I've asked this question on discourse.

[stevengj]

FFTW doesn't support this operation, so there is nothing we could implement here that would be faster than just doing the scaling etcetera yourself.

[ranocha]

Okay, thanks.