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Simplify fft full normalization #663

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merged 8 commits into from
Oct 15, 2024
Merged

Simplify fft full normalization #663

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b09b2ba
Make a 1d full normalization
tpadioleau Oct 13, 2024
c9a0854
Remove usage of the select function
tpadioleau Oct 13, 2024
72bce1b
Rename template parameters
tpadioleau Oct 13, 2024
09439ae
Use rlength
tpadioleau Oct 13, 2024
a6f9f52
Reorganize computation
tpadioleau Oct 13, 2024
4520b94
Reuse forward_full_norm_coef
tpadioleau Oct 13, 2024
2a1cb65
Use value instead of get
tpadioleau Oct 13, 2024
4c95c14
Review from Yuuichi
tpadioleau Oct 15, 2024
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29 changes: 16 additions & 13 deletions include/ddc/kernels/fft.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -176,6 +176,18 @@ void rescale(
});
}

template <class DDim>
Real forward_full_norm_coef(DiscreteDomain<DDim> const& ddom) noexcept
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{
return rlength(ddom) / Kokkos::sqrt(2 * Kokkos::numbers::pi) / (ddom.extents() - 1).value();
}

template <class DDim>
Real backward_full_norm_coef(DiscreteDomain<DDim> const& ddom) noexcept
{
return 1 / (forward_full_norm_coef(ddom) * ddom.extents().value());
}

/// @brief Core internal function to perform the FFT.
template <
typename Tin,
Expand Down Expand Up @@ -257,20 +269,11 @@ void impl(
if (kwargs.normalization == ddc::FFT_Normalization::FULL) {
real_type_t<Tout> norm_coef;
if (kwargs.direction == ddc::FFT_Direction::FORWARD) {
norm_coef
= (((coordinate(ddc::select<DDimIn>(in.domain()).back())
- coordinate(ddc::select<DDimIn>(in.domain()).front()))
/ (ddc::get<DDimIn>(in.domain().extents()) - 1)
/ Kokkos::sqrt(2 * Kokkos::numbers::pi))
* ...);
DiscreteDomain<DDimIn...> const ddom_in = in.domain();
norm_coef = (forward_full_norm_coef(DiscreteDomain<DDimIn>(ddom_in)) * ...);
} else {
norm_coef
= ((Kokkos::sqrt(2 * Kokkos::numbers::pi)
/ (coordinate(ddc::select<DDimOut>(out.domain()).back())
- coordinate(ddc::select<DDimOut>(out.domain()).front()))
* (ddc::get<DDimOut>(out.domain().extents()) - 1)
/ ddc::get<DDimOut>(out.domain().extents()))
* ...);
DiscreteDomain<DDimOut...> const ddom_out = out.domain();
norm_coef = (backward_full_norm_coef(DiscreteDomain<DDimOut>(ddom_out)) * ...);
}

rescale(exec_space, out, norm_coef);
Expand Down