dets.hpp

// Copyright (c) 2017--present, The Simons Foundation
// This file is part of TRIQS/ctint and is licensed under the terms of GPLv3 or later.
// SPDX-License-Identifier: GPL-3.0-or-later
// See LICENSE in the root of this distribution for details.
 
#pragma once
 
#include <ostream>
 
namespace triqs_ctint {
 
  using triqs::det_manip::det_manip;
 
  //------------------------------------

  template <bool dag> struct arg_t {

    static constexpr bool dagger = dag;

    tau_t tau;

    int u;

    int vertex_label = 0;

    int pos = 0;

    int s = 0;

    bool operator<(arg_t const &x) const { return std::tie(tau, u, vertex_label, pos, s) < std::tie(x.tau, x.u, x.vertex_label, x.pos, x.s); }
  };
 
  using c_t    = arg_t<false>;
  using cdag_t = arg_t<true>;
 
  template <bool dag> std::ostream &operator<<(std::ostream &os, arg_t<dag> const &c) {
    os << (c.dagger ? "cdag_t{" : "c_t{") << "tau=" << c.tau << ", "
       << "u=" << c.u << ", "
       << "vertex_label=" << c.vertex_label << ", "
       << "pos=" << c.pos << ", "
       << "s=" << c.s << "}";
    return os;
  }

  struct G0hat_t {
    gf_const_view<imtime, g_tau_t::target_t> G0_shift_tau;

    array_const_view<double, 4> alpha;
 
    g_tau_t::target_t::scalar_t operator()(c_t const &c, cdag_t const &cdag) const {
      // Contractions between operators of the same vertex get an alpha shift
      // Use tau-equality to check if cdag and c are from the same vertex
      if (c.tau == cdag.tau) {
        auto res = G0_shift_tau[0](c.u, cdag.u) + (c.u == cdag.u ? 1 : 0) - alpha(c.vertex_label, cdag.pos, c.pos, c.s);
        return res;
      }
      auto [s, dtau] = cyclic_difference(c.tau, cdag.tau);
      auto res       = G0_shift_tau[closest_mesh_pt(dtau)](c.u, cdag.u);
      // For the equal-time case, consider the order <c cdag>
      return s * res;
    }
  };

  using det_t = det_manip<G0hat_t>;
 
} // namespace triqs_ctint