swap_spin_lines.cpp

// Copyright (c) 2022--present, The Simons Foundation
// Copyright (c) 2022--present, Max Planck Institute for Polymer Research, Mainz, Germany
// This file is part of TRIQS/ctseg 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.
 
#include "swap_spin_lines.hpp"
#include "../logs.hpp"
#include <cmath>
 
namespace triqs_ctseg::moves {
 
  double swap_spin_lines::attempt() {
 
    LOG("\n =================== ATTEMPT SWAP SPIN LINES ================ \n");
 
    // ------------ Choose two spin lines --------------
 
    auto &jl = config.Jperp_list;
 
    if (jl.empty() or jl.size() == 1) {
      LOG("Nothing to swap!");
      return 0;
    }
 
    first_line_idx  = rng(jl.size());
    second_line_idx = rng(jl.size() - 1);
    if (second_line_idx >= first_line_idx) ++second_line_idx; // trick to select second_line_idx ! = first_line_idx
 
    auto &l1 = jl[first_line_idx];
    auto &l2 = jl[second_line_idx];
 
    // ------------  Trace ratio  -------------
 
    double J_current =                                                 //
       real(wdata.Jperp(double(l1.tau_Sminus - l1.tau_Splus))(0, 0)) * //
       real(wdata.Jperp(double(l2.tau_Sminus - l2.tau_Splus))(0, 0));
 
    double J_future =                                                  //
       real(wdata.Jperp(double(l1.tau_Sminus - l2.tau_Splus))(0, 0)) * //
       real(wdata.Jperp(double(l2.tau_Sminus - l1.tau_Splus))(0, 0));
 
    double trace_ratio = J_future / J_current;
 
    // ------------  Det ratio  ---------------
 
    double det_ratio = 1.0;
 
    // ------------  Proposition ratio ------------
 
    double prop_ratio = 1.0;
 
    LOG("trace_ratio  = {}, prop_ratio = {}, det_ratio = {}", trace_ratio, prop_ratio, det_ratio);
 
    double prod = trace_ratio * det_ratio * prop_ratio;
    return (std::isfinite(prod) ? prod : 1);
  }
 
  // --------------------------------------------
 
  double swap_spin_lines::accept() {
 
    LOG("\n - - - - - ====> ACCEPT - - - - - - - - - - -\n");
 
    auto &jl = config.Jperp_list;
    auto &l1 = jl[first_line_idx];
    auto &l2 = jl[second_line_idx];
 
    // Swap lines
    std::swap(l1.tau_Splus, l2.tau_Splus);
 
    // Check invariant
    if constexpr (print_logs or ctseg_debug) check_invariant(config, wdata);
    LOG("Configuration is {}", config);
 
    return 1.0;
  }
 
  //--------------------------------------------------
  void swap_spin_lines::reject() { LOG("\n - - - - - ====> REJECT - - - - - - - - - - -\n"); }
 
} // namespace triqs_ctseg::moves