Jungfraujoch/rugnux/LeftoverLattices.cpp

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

#include "LeftoverLattices.h"

#include <algorithm>
#include <cmath>
#include <Eigen/Dense>
#include "../common/JFJochMath.h"   // PI

const char *LeftoverLatticeKindName(LeftoverLatticeKind kind) {
    switch (kind) {
        case LeftoverLatticeKind::Self: return "SELF";
        case LeftoverLatticeKind::Domain: return "DOMAIN";
        case LeftoverLatticeKind::TwinDomain: return "TWIN_DOMAIN";
        case LeftoverLatticeKind::Segmented: return "SEGMENTED";
        case LeftoverLatticeKind::RelatedCell: return "RELATED_CELL";
        case LeftoverLatticeKind::Foreign: return "FOREIGN";
    }
    return "FOREIGN";
}

double LatticeMisorientationDeg(const CrystalLattice &a, const CrystalLattice &b) {
    auto mat = [](const CrystalLattice &l) {
        Eigen::Matrix3d M;
        const Coord v[3] = {l.Vec0(), l.Vec1(), l.Vec2()};
        for (int c = 0; c < 3; c++)
            M.col(c) = Eigen::Vector3d(v[c].x, v[c].y, v[c].z);
        return M;
    };
    const Eigen::Matrix3d A = mat(a), B = mat(b);
    const Eigen::Matrix3d GA = A.transpose() * A;
    const double scale = GA.diagonal().mean();
    // Every unimodular change of basis with entries -1..1: enough for two reduced cells.
    double best = NAN;
    for (int code = 0; code < 19683; code++) {
        Eigen::Matrix3d M;
        int c = code;
        for (int e = 0; e < 9; e++) {
            M(e / 3, e % 3) = c % 3 - 1;
            c /= 3;
        }
        if (std::abs(M.determinant() - 1.0) > 1e-6)
            continue;
        const Eigen::Matrix3d BM = B * M;
        if ((BM.transpose() * BM - GA).cwiseAbs().maxCoeff() > 0.06 * scale)
            continue;
        // The rotation nearest to the (slightly non-orthogonal) map from A to BM.
        Eigen::JacobiSVD<Eigen::Matrix3d> svd(BM * A.inverse(), Eigen::ComputeFullU | Eigen::ComputeFullV);
        const Eigen::Matrix3d R = svd.matrixU() * svd.matrixV().transpose();
        if (R.determinant() < 0)
            continue;
        const double ang = std::acos(std::clamp((R.trace() - 1.0) / 2.0, -1.0, 1.0)) * 180.0 / PI;
        if (std::isnan(best) || ang < best)
            best = ang;
    }
    return best;
}

LeftoverLatticeKind ClassifyLeftoverLattice(double misorientation_deg, double volume_ratio,
                                            double sweep_concentration) {
    if (std::isfinite(misorientation_deg)) {
        if (misorientation_deg <= 1.0)
            return LeftoverLatticeKind::Self;
        if (sweep_concentration >= 0.6)
            return LeftoverLatticeKind::Segmented;
        if (misorientation_deg >= 177.0)
            return LeftoverLatticeKind::TwinDomain;
        return LeftoverLatticeKind::Domain;
    }
    for (int n = 1; n <= 8; n++)
        if (std::abs(volume_ratio / n - 1.0) < 0.06 || std::abs(volume_ratio * n - 1.0) < 0.06)
            return LeftoverLatticeKind::RelatedCell;
    return LeftoverLatticeKind::Foreign;
}