refreq_pts.hpp

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// Copyright (c) 2019-2025 Simons Foundation
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You may obtain a copy of the License at
//     https://www.gnu.org/licenses/gpl-3.0.txt
//
// Authors: Rok Zitko, Nils Wentzell

 
#pragma once
 
#include "./mesh_iterator.hpp"
#include "./utils.hpp"
#include "../utility/exceptions.hpp"
#include "../utility/macros.hpp"
 
#include <fmt/format.h>
#include <h5/h5.hpp>
 
#include <algorithm>
#include <cmath>
#include <cstdint>
#include <initializer_list>
#include <iostream>
#include <numeric>
#include <string>
#include <vector>
 
namespace triqs::mesh {


  class C2PY_RENAME(MeshReFreqPts) refreq_pts {
    public:
    using value_t = double;

    using index_t = long;

    using data_index_t = long;

    class C2PY_IGNORE mesh_point_t {
      public:
      using mesh_t = refreq_pts;

      mesh_point_t() = default;

      mesh_point_t(long n, long d, uint64_t mhash, double w) : index_(n), data_index_(d), mesh_hash_(mhash), value_(w) {}

      [[nodiscard]] long index() const noexcept { return index_; }

      [[nodiscard]] long data_index() const noexcept { return data_index_; }

      [[nodiscard]] double value() const noexcept { return value_; }

      [[nodiscard]] uint64_t mesh_hash() const noexcept { return mesh_hash_; }

      operator double() const { return value_; } // NOLINT (implicit conversion intended)
 
      // Arithmetic operations with scalars.
#define IMPL_OP(OP)                                                                                                                                  \
  template <typename U> friend auto operator OP(mesh_point_t const &mp, U &&y) { return mp.value() OP std::forward<U>(y); }                          \
  template <typename U>                                                                                                                              \
    requires(not std::is_same_v<std::decay_t<U>, mesh_point_t>)                                                                                      \
  friend auto operator OP(U &&x, mesh_point_t const &mp) {                                                                                           \
    return std::forward<U>(x) OP mp.value();                                                                                                         \
  }
      IMPL_OP(+)
      IMPL_OP(-)
      IMPL_OP(*)
      IMPL_OP(/)
#undef IMPL_OP
 
      private:
      long index_         = 0;
      long data_index_    = 0;
      uint64_t mesh_hash_ = 0;
      double value_       = 0.0;
    };

    refreq_pts() = default;

    refreq_pts(std::vector<double> pts)
       : pts_(std::move(pts)),
         mesh_hash_(hash(std::accumulate(pts_.begin(), pts_.end(), 0.0), pts_.empty() ? 0.0 : pts_.front(), pts_.empty() ? 0.0 : pts_.back(),
                         static_cast<long>(pts_.size()))) {
      if (not std::ranges::is_sorted(pts_)) TRIQS_RUNTIME_ERROR << "refreq_pts mesh must be constructed with a sorted list of points";
    }

    C2PY_IGNORE refreq_pts(std::initializer_list<double> l) : refreq_pts(std::vector<double>(l)) {}

    bool operator==(refreq_pts const &) const = default;

    [[nodiscard]] bool is_index_valid(index_t n) const noexcept { return 0 <= n and n < size(); }

    [[nodiscard]] bool is_value_valid(double w) const noexcept { return !pts_.empty() and pts_.front() <= w and w <= pts_.back(); }

    [[nodiscard]] data_index_t to_data_index(index_t n) const noexcept {
      EXPECTS(is_index_valid(n));
      return n;
    }

    [[nodiscard]] C2PY_IGNORE data_index_t to_data_index(closest_mesh_point_t<double> const &cmp) const noexcept {
      return to_data_index(to_index(cmp));
    }

    [[nodiscard]] index_t to_index(data_index_t d) const noexcept {
      EXPECTS(is_index_valid(d));
      return d;
    }

    [[nodiscard]] C2PY_IGNORE index_t to_index(closest_mesh_point_t<double> const &cmp) const noexcept {
      EXPECTS(is_value_valid(cmp.value));
 
      auto itr_r = std::ranges::lower_bound(pts_, cmp.value);
      long i_r   = itr_r - pts_.begin();
 
      if (i_r == 0) { return 0; }
      if (i_r == size()) { return size() - 1; }
 
      long i_l = i_r - 1;
      if (std::abs(cmp.value - pts_[i_l]) < std::abs(cmp.value - pts_[i_r]))
        return i_l;
      else
        return i_r;
    }

    [[nodiscard]] mesh_point_t operator[](long d) const noexcept { return (*this)(d); }

    [[nodiscard]] C2PY_IGNORE mesh_point_t operator[](closest_mesh_point_t<double> const &cmp) const noexcept { return (*this)[to_data_index(cmp)]; }

    [[nodiscard]] mesh_point_t operator()(index_t n) const noexcept {
      EXPECTS(is_index_valid(n));
      return {n, n, mesh_hash_, pts_[n]};
    }

    [[nodiscard]] double to_value(index_t n) const noexcept {
      EXPECTS(is_index_valid(n));
      return pts_[n];
    }

    [[nodiscard]] C2PY_PROPERTY_GET(mesh_hash) uint64_t mesh_hash() const noexcept { return mesh_hash_; }

    [[nodiscard]] long size() const noexcept { return static_cast<long>(pts_.size()); }

    [[nodiscard]] C2PY_PROPERTY_GET(points) std::vector<double> const &points() const noexcept { return pts_; }

    [[nodiscard]] auto begin() const { return mesh_iterator<refreq_pts>{.mesh_ptr = this, .data_index = 0}; }

    [[nodiscard]] auto cbegin() const { return begin(); }

    [[nodiscard]] auto end() const { return mesh_iterator<refreq_pts>{.mesh_ptr = this, .data_index = size()}; }

    [[nodiscard]] auto cend() const { return end(); }

    friend std::ostream &operator<<(std::ostream &sout, refreq_pts const &m) {
      return sout << fmt::format("Real frequency point mesh of size {}", m.size());
    }

    void serialize(auto &ar) const { ar & pts_ & mesh_hash_; }

    void deserialize(auto &ar) { ar & pts_ & mesh_hash_; }

    [[nodiscard]] static std::string hdf5_format() { return "MeshReFreqPts"; }

    friend void h5_write(h5::group g, std::string const &name, refreq_pts const &m) {
      h5::group gr = g.create_group(name);
      h5::write_hdf5_format(gr, m); // NOLINT (downcasting to base class)
      h5::write(gr, "points", m.pts_);
    }

    friend void h5_read(h5::group g, std::string const &name, refreq_pts &m) {
      h5::group gr = g.open_group(name);
      h5::assert_hdf5_format(gr, m, true); // NOLINT (downcasting to base class)
      auto pts = h5::read<std::vector<double>>(gr, "points");
      m        = refreq_pts(std::move(pts));
    }
 
    private:
    std::vector<double> pts_;
    uint64_t mesh_hash_ = 0;
  };

  inline auto evaluate(refreq_pts const &m, auto const &f, double w) {
    EXPECTS(m.is_value_valid(w));
 
    auto const &pts = m.points();
    auto itr_r      = std::ranges::lower_bound(pts, w);
    long i_r        = itr_r - pts.begin();
 
    if (i_r == 0) { return f(0); }
    if (i_r == m.size()) { return f(m.size() - 1); }
 
    long i_l = i_r - 1;
 
    double w_l = pts[i_l];
    double w_r = pts[i_r];
    double del = w_r - w_l;
 
    double wt_r = (w - w_l) / del;
    double wt_l = (w_r - w) / del;
 
    return f(i_l) * wt_l + f(i_r) * wt_r;
  }

 
} // namespace triqs::mesh