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Adds function to conveniently obtain the real part of the inverse. #186

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Merged
sebsjames merged 1 commit into from
Sep 23, 2026
Merged

Adds function to conveniently obtain the real part of the inverse. #186

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11 changes: 11 additions & 0 deletions sm/hexfft.cppm
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Original file line number Diff line number Diff line change
Expand Up @@ -408,6 +408,17 @@ export namespace sm::hexfft
return this->image_asa_to_hexgrid();
}

//! Return the real component of the inverse FFT.
sm::vvec<F> inverse_real()
{
sm::vvec<std::complex<F>> inv_cplx = this->inverse();
sm::vvec<F> inv_real (inv_cplx.size(), F{0});
for (std::uint32_t i = 0; i < inv_cplx.size(); ++i) {
inv_real[i] = std::real (inv_cplx[i]);
}
return inv_real;
}

private:

//! Find parameters for the enclosing hexgrid (used to populate d0/d1 and create hg_asa)
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4 changes: 4 additions & 0 deletions tests/hexfft1.cpp
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Expand Up @@ -27,10 +27,14 @@ static bool roundtrips (sm::hexgrid<F>& hg, const char* label)
sm::hexfft::fft<F> hfft (&hg, data);
sm::vvec<std::complex<F>> back = hfft.inverse();

sm::vvec<F> back_real = hfft.inverse_real();

F maxerr = F{0};
for (std::uint32_t i = 0; i < hg.num(); ++i) {
F err = std::abs (back[i] - std::complex<F> (data[i], F{0}));
F err_real = std::abs (back_real[i] - data[i]);
maxerr = std::max (maxerr, err);
maxerr = std::max (maxerr, err_real);
}
std::cout << label << ": hg.num()=" << hg.num() << " spectrum rows=" << hfft.asa_rows << " cols=" << hfft.asa_cols
<< " (size " << hfft.size() << ") max roundtrip error: " << maxerr << std::endl;
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