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Potentially suboptimal performance in r2r transforms? #189

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jishnub opened this issue Nov 15, 2022 · 1 comment
Open

Potentially suboptimal performance in r2r transforms? #189

jishnub opened this issue Nov 15, 2022 · 1 comment

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@jishnub
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jishnub commented Nov 15, 2022

Currently, the Chebyshev plans internally use FFTW.r2r plans, eg.

function plan_chebyshevtransform(x::AbstractArray{T,N}, ::Val{1}, dims...; kws...) where {T<:fftwNumber,N}
if isempty(x)
ChebyshevTransformPlan{T,1,kindtuple(FIRSTKIND,N,dims...),false,N,isempty(dims) ? UnitRange{Int} : typeof(dims)}()
else
ChebyshevTransformPlan{T,1,kindtuple(FIRSTKIND,N,dims...)}(FFTW.plan_r2r(x, FIRSTKIND, dims...; kws...))
end
end

However, from what I understand after reading Steven G. Johnson's post on discourse, the r2r transforms are not as optimized as the r2c ones, and are not recommended over the alternatives. I wonder if a rewrite of the r2r transforms (here or elsewhere) might improve performance?

@MikaelSlevinsky
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I guess it could be worth benchmarking, though it feels more like an FFTW issue to me.

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