Jungfraujoch/rugnux/ModelFFT.h

// SPDX-FileCopyrightText: 2026 Filip Leonarski, Paul Scherrer Institute <filip.leonarski@psi.ch>
// SPDX-License-Identifier: GPL-3.0-only

#pragma once

#include "gemmi/grid.hpp"
#include "gemmi/recgrid.hpp"

// The structure factors of a real-space map on the model path (Fcalc from the model density, Fmask
// from the bulk-solvent mask): what gemmi::transform_map_to_f_phi(map, true) returns - the
// conjugated forward transform (F = sum rho exp(+2 pi i h.x)) scaled by V/N, kept for l >= 0 on an (nu, nv, nw/2+1) grid in the map's own XYZ order,
// ready for prepare_asu_data() - computed with FFTW rather than gemmi's single-threaded pocketfft.
// The same transform, not the same bits: the two libraries order their arithmetic differently.
//
// Plans are FFTW_ESTIMATE only - MEASURE would time candidate algorithms and could pick a different
// one from run to run - and made once per grid size and kept, so the rigid body's hundred-odd
// evaluations on one grid plan once. Safe to call from several threads at once.
gemmi::FPhiGrid<float> MapToFPhi(const gemmi::Grid<float> &map);

// The inverse: the real-space map of an (nu, nv, nw/2+1) half-l coefficient grid in XYZ order, as
// get_f_phi_on_grid() fills it - what gemmi::transform_f_phi_grid_to_map() returns (rho = 1/V sum F
// exp(-2 pi i h.x) on an (nu, nv, 2*(nw-1)) grid, NaN coefficients read as zero), computed with FFTW
// under the same planning rules.
gemmi::Grid<float> MapFromFPhi(const gemmi::FPhiGrid<float> &hkl);