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fft normalization test (#152)
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* fft normalization test

* increase criterion

* wip

* feedbacks

* test independant of mesh resolution

* Change name convention _f -> f_alloc for Chunk

* remove host copy in fft_norm test

* get_domain -> domain()

* clangd-format
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@blegouix
blegouix authored Jul 19, 2023
1 parent 130e914 commit 396f28f
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Showing 2 changed files with 127 additions and 6 deletions.
51 changes: 51 additions & 0 deletions tests/fft.cpp
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
// SPDX-License-Identifier: MIT

#include <ddc/ddc.hpp>
#include <ddc/kernels/fft.hpp>

#include <gtest/gtest.h>

Expand All @@ -10,6 +11,56 @@ struct RDimX;
struct RDimY;
struct RDimZ;

TEST(FFTNorm, OFF)
{
test_fft_norm<
Kokkos::Serial,
Kokkos::Serial::memory_space,
float,
Kokkos::complex<float>,
RDimX>(ddc::FFT_Normalization::OFF);
}

TEST(FFTNorm, BACKWARD)
{
test_fft_norm<
Kokkos::Serial,
Kokkos::Serial::memory_space,
float,
Kokkos::complex<float>,
RDimX>(ddc::FFT_Normalization::BACKWARD);
}

TEST(FFTNorm, FORWARD)
{
test_fft_norm<
Kokkos::Serial,
Kokkos::Serial::memory_space,
float,
Kokkos::complex<float>,
RDimX>(ddc::FFT_Normalization::FORWARD);
}

TEST(FFTNorm, ORTHO)
{
test_fft_norm<
Kokkos::Serial,
Kokkos::Serial::memory_space,
float,
Kokkos::complex<float>,
RDimX>(ddc::FFT_Normalization::ORTHO);
}

TEST(FFTNorm, FULL)
{
test_fft_norm<
Kokkos::Serial,
Kokkos::Serial::memory_space,
float,
Kokkos::complex<float>,
RDimX>(ddc::FFT_Normalization::FULL);
}

TEST(FFTSerialHost, R2C_1D)
{
test_fft<Kokkos::Serial, Kokkos::Serial::memory_space, float, Kokkos::complex<float>, RDimX>();
Expand Down
82 changes: 76 additions & 6 deletions tests/fft.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -63,9 +63,8 @@ static void test_fft()
double const xn2 = (Kokkos::pow(ddc::coordinate(ddc::select<DDim<X>>(e)), 2) + ...);
f(e) = Kokkos::exp(-xn2 / 2);
});

ddc::Chunk _f_bis(f.domain(), ddc::KokkosAllocator<Tin, MemorySpace>());
ddc::ChunkSpan f_bis = _f_bis.span_view();
ddc::Chunk f_bis_alloc(f.domain(), ddc::KokkosAllocator<Tin, MemorySpace>());
ddc::ChunkSpan f_bis = f_bis_alloc.span_view();
ddc::deepcopy(f_bis, f);

ddc::Chunk Ff_alloc(k_mesh, ddc::KokkosAllocator<Tout, MemorySpace>());
Expand All @@ -82,8 +81,8 @@ static void test_fft()
ddc::ChunkSpan FFf = FFf_alloc.span_view();
ddc::ifft(ExecSpace(), FFf, Ff_bis, {ddc::FFT_Normalization::FULL});

ddc::Chunk _f_host(f.domain(), ddc::HostAllocator<Tin>());
ddc::ChunkSpan f_host = _f_host.span_view();
ddc::Chunk f_host_alloc(f.domain(), ddc::HostAllocator<Tin>());
ddc::ChunkSpan f_host = f_host_alloc.span_view();
ddc::deepcopy(f_host, f);

ddc::Chunk Ff_host_alloc(Ff.domain(), ddc::HostAllocator<Tout>());
Expand Down Expand Up @@ -120,10 +119,81 @@ static void test_fft()
double const diff = Kokkos::abs(FFf_host(e)) - Kokkos::abs(f_host(e));
return pow2(diff) / Kokkos::pow(Nx, sizeof...(X));
}));

double epsilon = std::is_same_v<ddc::detail::fft::real_type_t<Tin>, double> ? 1e-15 : 1e-7;
ASSERT_LE(criterion, epsilon)
<< "Distance between analytical prediction and numerical result : " << criterion;
ASSERT_LE(criterion2, epsilon)
<< "Distance between input and iFFT(FFT(input)) : " << criterion2;
}

template <typename ExecSpace, typename MemorySpace, typename Tin, typename Tout, typename X>
static void test_fft_norm(ddc::FFT_Normalization const norm)
{
constexpr bool full_fft
= ddc::detail::fft::is_complex_v<Tin> && ddc::detail::fft::is_complex_v<Tout>;

DDom<DDim<X>> const x_mesh = ddc::init_discrete_space(DDim<X>::
init(ddc::Coordinate<X>(-1. / 4),
ddc::Coordinate<X>(1. / 4),
DVect<DDim<X>>(2)));
ddc::init_fourier_space<X>(x_mesh);
DDom<DFDim<ddc::Fourier<X>>> const k_mesh = ddc::FourierMesh(x_mesh, full_fft);

ddc::Chunk f_alloc = ddc::Chunk(x_mesh, ddc::KokkosAllocator<Tin, MemorySpace>());
ddc::ChunkSpan f = f_alloc.span_view();
ddc::for_each(
policy<ExecSpace>(),
f.domain(),
DDC_LAMBDA(DElem<DDim<X>> const e) { f(e) = static_cast<Tin>(1); });


ddc::Chunk f_bis_alloc = ddc::Chunk(f.domain(), ddc::KokkosAllocator<Tin, MemorySpace>());
ddc::ChunkSpan f_bis = f_bis_alloc.span_view();
ddc::deepcopy(f_bis, f);

ddc::Chunk Ff_alloc = ddc::Chunk(k_mesh, ddc::KokkosAllocator<Tout, MemorySpace>());
ddc::ChunkSpan Ff = Ff_alloc.span_view();
ddc::fft(ExecSpace(), Ff, f_bis, {norm});
Kokkos::fence();

// deepcopy of Ff because FFT C2R overwrites the input
ddc::Chunk Ff_bis_alloc = ddc::Chunk(Ff.domain(), ddc::KokkosAllocator<Tout, MemorySpace>());
ddc::ChunkSpan Ff_bis = Ff_bis_alloc.span_view();
ddc::deepcopy(Ff_bis, Ff);

ddc::Chunk FFf_alloc = ddc::Chunk(x_mesh, ddc::KokkosAllocator<Tin, MemorySpace>());
ddc::ChunkSpan FFf = FFf_alloc.span_view();
ddc::ifft(ExecSpace(), FFf, Ff_bis, {norm});

double const f_sum = ddc::transform_reduce(f.domain(), 0., ddc::reducer::sum<double>(), f);

double Ff0_expected;
double FFf_expected;
switch (norm) {
case ddc::FFT_Normalization::OFF:
Ff0_expected = f_sum;
FFf_expected = f_sum;
break;
case ddc::FFT_Normalization::FORWARD:
Ff0_expected = 1;
FFf_expected = 1;
break;
case ddc::FFT_Normalization::BACKWARD:
Ff0_expected = f_sum;
FFf_expected = 1;
break;
case ddc::FFT_Normalization::ORTHO:
Ff0_expected = Kokkos::sqrt(f_sum);
FFf_expected = 1;
break;
case ddc::FFT_Normalization::FULL:
Ff0_expected = 1 / Kokkos::sqrt(2 * Kokkos::numbers::pi);
FFf_expected = 1;
break;
}

double epsilon = 1e-6;
EXPECT_NEAR(Kokkos::abs(Ff(Ff.domain().front())), Ff0_expected, epsilon);
EXPECT_NEAR(FFf(FFf.domain().front()), FFf_expected, epsilon);
EXPECT_NEAR(FFf(FFf.domain().back()), FFf_expected, epsilon);
}

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