Jungfraujoch/image_analysis/structure_refinement/RefinementXray.h

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

#pragma once

#include <array>
#include <complex>
#include <memory>
#include <optional>
#include <vector>

#include "gemmi/grid.hpp"
#include "gemmi/model.hpp"
#include "gemmi/symmetry.hpp"
#include "gemmi/unitcell.hpp"

#include "../../common/Reflection.h"   // MergedReflection
#include "RefinementRestraints.h"     // RestraintSet
#include "RigidBodyRefine.h"           // SymmetryComposition

// The X-ray side of restrained refinement (Refinement.h): the observed amplitudes, the model's structure
// factors and the maximum-likelihood target that compares them, with its gradient with respect to every
// atom's position and B.

// The reflections a refinement fits and scores: the observed amplitudes, in the group's reciprocal ASU, that
// the refinement grid composes (SymmetryComposition) - every observed one in practice.
struct RefinementReflections {
    std::vector<gemmi::Miller> hkl;
    std::vector<float> fo, sigma;
    std::vector<char> free, centric;
    std::vector<float> epsilon;
    std::vector<double> inv_d2;
    size_t Size() const { return hkl.size(); }
};

// The French-Wilson amplitudes of `merged` (NaN dropped) into the ASU of `sg`, those the grid of
// RigidBodyZoneGrid(cell, sg, d_min) composes.
RefinementReflections PrepareRefinementReflections(const std::vector<MergedReflection> &merged,
                                                   const gemmi::UnitCell &cell, const gemmi::SpaceGroup &sg,
                                                   double d_min);

// What turns the atoms' structure factors F into the model the target compares with the data, per reflection:
//   F_model = k_total (F + fmask),
// with k_total the overall scale and anisotropic B and fmask the bulk solvent already scaled by k_sol
// exp(-b_sol s^2/4); and the two parameters of the likelihood, D and the variance. Fixed for one macro-cycle.
struct XrayRowModel {
    std::vector<float> k_total;
    std::vector<std::complex<float>> fmask;
    std::vector<float> d, var;
};

// The ML parameters per reflection from the free reflections: D and beta fitted by maximum likelihood in
// resolution bins of the free set and interpolated between the bins' centres; the variance of a reflection is
// epsilon beta + sigma^2. `fmodel` is k_total (F + fmask), without D.
// Following Lunin & Skovoroda (1995) Acta Cryst. A51, 880-887, and Afonine et al. (2012) Acta Cryst. D68, 352-367
void EstimateLikelihoodParameters(const RefinementReflections &refl, const std::vector<std::complex<float>> &fmodel,
                                  XrayRowModel &rows);

// R-work and R-free of k_total (F + fmask) against the observations.
struct RFactors {
    double r_work = 1, r_free = 1;
    int n_work = 0, n_free = 0;
};
RFactors ComputeRFactors(const RefinementReflections &refl, const std::vector<std::complex<float>> &fmodel);

// What evaluates the targets for a set of atom positions and B: the CPU below, or a GPU (RefinementGPU.h). The
// atoms are the model's, all of them, in model order; the grid and the reflections are fixed when the engine is
// made, the row model each macro-cycle, the blur where SetBlur is called.
class RefinementEngine {
public:
    virtual ~RefinementEngine() = default;
    // The blur the atoms are gridded with (DensityCalculator's), and the matching unblur of their transform.
    // Every atom's B must stay above what the blur was chosen for (RefinementBlur) while it is in use.
    virtual void SetBlur(double blur) = 0;
    virtual void SetRowModel(const XrayRowModel &rows) = 0;
    // F of the atoms at the reflections.
    virtual void Fcalc(const gemmi::Model &model, std::vector<std::complex<float>> &f) = 0;
    // The bulk-solvent mask's structure factors at the reflections (unscaled).
    virtual void Fmask(const gemmi::Model &model, std::vector<std::complex<float>> &f) = 0;
    // The sum of -ln L over the working reflections and, with `grad`, its derivatives with respect to every
    // atom's x, y, z (Cartesian, A) and B (A^2), in model order.
    virtual double Evaluate(const gemmi::Model &model, std::vector<std::array<double, 4>> *grad) = 0;
    virtual bool OnGPU() const = 0;

    // Restraint set `which` (0: the geometry and the repulsions, 1: the B similarity) and its sum of E at xyzb
    // (x, y, z, B per atom) with, given `grad`, dE/d(x, y, z, B) per atom. On the CPU unless the engine has its own.
    virtual void SetRestraints(int which, const RestraintSet &set) { restraints_[which] = set; }
    virtual double EvaluateRestraints(int which, const std::vector<std::array<double, 4>> &xyzb,
                                      std::vector<std::array<double, 4>> *grad) {
        if (grad != nullptr)
            grad->assign(xyzb.size(), {0, 0, 0, 0});
        return ::EvaluateRestraints(restraints_[which], xyzb, grad);
    }

private:
    RestraintSet restraints_[2];
};

// The blur for a model whose smallest B may go as low as b_floor: DensityCalculator's
// set_refmac_compatible_blur() for that B, on the refinement grid of d_min.
double RefinementBlur(const gemmi::UnitCell &cell, const gemmi::SpaceGroup &sg, double d_min, double b_floor);

// The CPU engine: the density of one copy of the atoms on the grid of RigidBodyZoneGrid(cell, sg, d_min)
// (PutModelDensityOnGrid), its transform and the crystal's symmetry composed in reciprocal space
// (SymmetryComposition). The gradient by the FFT method: the derivative of the target with respect to each
// structure factor, taken back to real space by one inverse transform, is a map; each atom's derivatives are
// that map summed against the derivatives of its own density.
// Following Agarwal (1978) Acta Cryst. A34, 791-809
std::unique_ptr<RefinementEngine> MakeRefinementEngineCPU(const gemmi::UnitCell &cell,
                                                          const gemmi::SpaceGroup &sg, double d_min,
                                                          const RefinementReflections &refl, size_t nthreads);

// The derivative map of the X-ray target on a grid (the FFT method's map), summed against each atom's density
// derivatives: dT/d(x, y, z, B) per atom. `map` is u fastest on the grid of RigidBodyZoneGrid(), the atoms
// gridded with `blur`. Exposed for the tests.
void AtomGradientsFromMap(const gemmi::Grid<float> &map, const gemmi::Model &model, double blur, size_t nthreads,
                          std::vector<std::array<double, 4>> &grad);