Jungfraujoch/image_analysis/scale_merge/AnisotropyAnalysis.h

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

#pragma once

#include <string>
#include <vector>

#include "../../common/Reflection.h"
#include "../IntegrationOutcome.h"
#include "gemmi/symmetry.hpp"
#include "gemmi/unitcell.hpp"

// Diffraction-anisotropy diagnostic. It DESCRIBES and it REPORTS: no intensity is corrected, no
// reflection is removed, and the written reflection file does not depend on direction in any way.
// Two quantities are reported, and they are not the same thing:
//
//   - the anisotropic deltaB, the range of the principal components of the anisotropy tensor (the
//     AIMLESS quantity), which is a RATE of fall-off;
//   - the diffraction limit along each principal direction, from <I/sigma(I)> in a cone about that
//     direction (the AIMLESS construction), which is where the signal actually runs out.
//
// A crystal can have a large deltaB and almost no spread in directional limit, or the reverse.
//
// CONVENTION. The tensor is fitted as ln <I(s)> = c(shell) - 1/2 s^T B s, s = 1/d in A^-1, B in A^2.
// For an isotropic B this is the ordinary Wilson plot, so B here is the ordinary crystallographic
// (structure-factor-level, B = 8 pi^2 U) B - the same scale as phenix.xtriage's B_cart, ctruncate's
// anisotropic B eigenvalues and AIMLESS's anisotropic deltaB, and directly comparable with all three.
// Only the DEVIATORIC part is fitted: the isotropic part is degenerate with the overall scale and with
// the Wilson curve, and one free constant per resolution shell absorbs it exactly.
//
// The tensor is fitted on INTENSITIES, with no positivity cut. Fitting amplitudes, or dropping
// non-positive intensities as the amplitude-based tools must, loses roughly 40% of the signal: in a
// direction that has died, half the merged intensities are negative, so a positivity cut keeps only
// the positive noise excursions and flattens the fall-off exactly where the anisotropy is largest.
//
// TWO INPUTS, because they answer different halves of the question. The tensor, its resolution
// signature and the directional limits are measured on the MERGED reflections. The error bar the
// verdict is gated on cannot be: merged data has exact Laue symmetry by construction, so the
// symmetry-forbidden tensor directions - where the true tensor is zero whatever the crystal is, and
// which are therefore this dataset's own measurement of its systematic error - are identically zero
// there. That measurement needs the UNMERGED, scaled observations, which still carry the differences
// between symmetry mates. Without them the verdict is "cannot determine" and says so.
//
// Method credits are at the algorithms in the .cpp.

enum class AnisotropyShape {
    Undetermined,   // too few shells, or the verdict moved when the binning changed
    Linear,         // the deficit follows exp(-1/2 s^T B s): a Debye-Waller B
    Flat,           // the deficit does not follow exp(-1/2 s^T B s) - see the note on Flat below
    Convex          // the deficit grows faster than s^2
};

enum class AnisotropyVerdict {
    CannotDetermine,   // this dataset cannot answer the question - `refusal` says why
    NotDetected,       // anisotropy is not established above this dataset's own systematic error
    Detected           // anisotropy is established; `band` grades it
};

const char *AnisotropyShapeCode(AnisotropyShape shape);       // e.g. "LINEAR"
const char *AnisotropyVerdictCode(AnisotropyVerdict verdict); // e.g. "NOT_DETECTED"

struct AnisotropyResult {
    // "Could not decide" is a counter, not a flag: every renderer tests n_reflections and falls silent
    // when it is zero (the TwinningAnalysis idiom). n_free_parameters is the deviatoric degrees of
    // freedom the Laue class allows - 5 triclinic, 3 monoclinic, 2 orthorhombic, 1 tetragonal/trigonal/
    // hexagonal, 0 cubic - so 0 means "no anisotropy is possible here", not "nothing was measured", and
    // a cubic crystal reports n_reflections > 0 with n_cells = 0 and deltaB exactly zero.
    int n_reflections = 0;
    int n_cells = 0;
    int n_free_parameters = 0;
    int n_observations = 0;      // unmerged observations the systematic-error floor was measured on

    // --- the tensor ---------------------------------------------------------------------------
    double delta_b = NAN;                 // B_max - B_min of the deviatoric tensor, A^2
    double eigenvalue[3] = {NAN, NAN, NAN};       // descending; deviatoric, so they sum to zero
    double eigenvector[3][3] = {{NAN, NAN, NAN}, {NAN, NAN, NAN}, {NAN, NAN, NAN}};  // Cartesian rows
    double fold_weakening = NAN;          // exp(delta_b / 2 d_min^2): strong/weak intensity ratio at d_min

    // --- the diffraction limits (model-free) --------------------------------------------------
    // Highest resolution at which <I/sigma(I)> in a 20 deg cone about principal axis n is still 2.0.
    double d_min_axis[3] = {NAN, NAN, NAN};
    // True when <I/sigma(I)> in that cone had not yet fallen to 2.0 at the edge of the measured data.
    // The value returned is then where the DATA stop, not where the signal does: it is a bound on the
    // limit, not a measurement of it, and d_min_spread built from it is a lower bound.
    bool d_min_censored[3] = {false, false, false};
    double d_min_spread = NAN;            // max - min of the above

    // --- the resolution signature of the deficit ----------------------------------------------
    // The l=2 directional deficit A of each shell against s^2, fitted as A = c0 + c1 s^2. A genuine
    // Debye-Waller B gives a straight line through the origin (c0 = 0, c1 = |B_dev|).
    int shape_shells = 0;
    double shape_intercept = NAN;         // c0, dimensionless
    double shape_intercept_z = NAN;       // c0 / sigma(c0)
    double shape_slope = NAN;             // c1, A^2
    double shape_curvature_z = NAN;       // significance of an s^4 term
    double shape_curvature_share = NAN;   // fraction of the deficit that term carries at the limit
    double shape_residual = NAN;          // chi2/dof of the through-origin line
    AnisotropyShape shape = AnisotropyShape::Undetermined;
    bool shape_stable = false;            // the verdict survived rebinning at 8 and 16 shells
    // deltaB implied by the s^2 slope alone - what a Debye-Waller B accounts for - and the rest.
    // The first can exceed delta_b when the fitted curve passes below the origin.
    double delta_b_linear = NAN;
    double delta_b_flat = NAN;

    // --- the gate -----------------------------------------------------------------------------
    // Everything here is measured from this dataset alone. sigma_systematic is the per-component
    // systematic error scale left in the symmetry-FORBIDDEN tensor directions of the unmerged
    // observations after their own counting noise has been taken out; floor is what that systematic,
    // plus counting noise, would manufacture in the symmetry-ALLOWED directions; significance is
    // delta_b_linear / floor.
    double sigma_systematic = NAN;
    // The scatter measured in the symmetry-FORBIDDEN directions over its own counting null. It is
    // normally well above 1 (a real dataset's forbidden subspace is dominated by systematics, not by
    // counting noise); it is large together with a gate that establishes nothing when a too-high Laue
    // class has pushed real anisotropy into those directions - R2's "space group suspect" signature.
    double forbidden_z = NAN;
    double floor = NAN;
    double significance = NAN;
    double detection_limit = NAN;         // the smallest delta_b this dataset could establish, A^2
    AnisotropyVerdict verdict = AnisotropyVerdict::CannotDetermine;
    std::string band;                     // "not established" / "marginal" / "established" / "strong"
    std::string refusal;                  // why, when the verdict is CannotDetermine
    std::vector<std::string> cautions;    // things that bias the verdict, each measured
};

// One scaled, unmerged observation: the Miller index it was measured at (NOT reduced to the
// asymmetric unit - the whole point is that symmetry mates are separate measurements) and its
// intensity on the merge's own scale.
struct AnisotropyObservation {
    int32_t h = 0, k = 0, l = 0;
    float I = NAN;
    float sigma = NAN;
    float d = NAN;
};

// Build those from the per-image integration outcomes, on the scale rugnux itself applied. On rotation
// data each reflection's partials are first assembled into one full, as the 3D combine and the
// unmerged export do; on stills each reflection is already a whole measurement. Images with no fitted
// per-image scale are left out, and so is an event that caught less than min_partiality of its rocking
// curve - the combine does not merge one either.
//
// Only a SAMPLE of the unique reflections is assembled on rotation data, because only a sample is ever
// looked at: the floor these feed is measured on a few tens of thousands of unique reflections and the
// analysis strides the rest away. `space_group` is the one that floor will be measured in, and the
// sample is of whole unique reflections in it - the floor is a contrast between symmetry mates, so a
// reflection is taken with all of its mates or not at all. Pass the space group AnalyzeAnisotropy will
// be given; a null one samples Friedel pairs, which is what that call then treats as triclinic.
std::vector<AnisotropyObservation> ScaledObservations(const std::vector<IntegrationOutcome> &outcomes,
                                                     bool rotation,
                                                     const gemmi::SpaceGroup *space_group = nullptr,
                                                     float wedge_deg = 0.0f,
                                                     double min_partiality = 0.5,
                                                     size_t nthreads = 1);

// What the caller knows about the run and the merge that the reflections alone do not say.
struct AnisotropyRunInfo {
    // Rotation actually covered by the processed images, in degrees (NOT the header's nominal sweep -
    // one battery dataset spans 179 deg against a 360 deg header). NaN for stills / not known.
    double observed_rotation_deg = NAN;
    // Whether the scale model that produced these intensities carried a dose (decay) term. Mandatory
    // on rotation data: see the note at the refusal in the .cpp.
    bool dose_term_in_scale_model = true;
    // The run's measured radiation damage (MergeStatistics::radiation_damage_delta_b), for the caution.
    double radiation_damage_relative_b = NAN;
};

AnisotropyResult AnalyzeAnisotropy(const std::vector<MergedReflection> &merged,
                                   const std::vector<AnisotropyObservation> &unmerged,
                                   const gemmi::UnitCell &cell,
                                   const gemmi::SpaceGroup *space_group,
                                   const AnisotropyRunInfo &run = {});

std::string AnisotropyToText(const AnisotropyResult &result);