dft_tools/triqs/gfs/domains/matsubara.hpp

/*******************************************************************************
 *
 * TRIQS: a Toolbox for Research in Interacting Quantum Systems
 *
 * Copyright (C) 2012 by M. Ferrero, O. Parcollet
 *
 * TRIQS 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.
 *
 * TRIQS 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 should have received a copy of the GNU General Public License along with
 * TRIQS. If not, see <http://www.gnu.org/licenses/>.
 *
 ******************************************************************************/
#pragma once
#include "../tools.hpp"
#include <triqs/utility/arithmetic_ops_by_cast.hpp>
#include <triqs/utility/kronecker.hpp>

namespace triqs {
namespace gfs {

 /** 
  * A matsubara frequency, i.e. 
  *   * n : int, the index
  *   * beta : double, the temperature inverse
  *   * statistic : Fermion or Boson
  *
  * * Can be casted into a complex.
  *
  * * Every operations is done by casting to complex, except addition and substraction of matsubara_freq, which return matsubara_freq
  *   and work on the index
  **/
 struct matsubara_freq : public utility::arithmetic_ops_by_cast_disable_same_type<matsubara_freq, std::complex<double>> {
  int n;
  double beta;
  statistic_enum statistic;
  matsubara_freq() : n(0), beta(1), statistic(Fermion) {}
  matsubara_freq(int n_, double beta_, statistic_enum stat_) : n(n_), beta(beta_), statistic(stat_) {}
  using cast_t = std::complex<double>;
  operator cast_t() const {
   return {0, M_PI * (2 * n + statistic) / beta};
  }
 };

 inline std::ostream &operator<<(std::ostream &out, matsubara_freq const &y) { return out << std::complex<double>(y); }

 inline matsubara_freq operator+(matsubara_freq const &x, matsubara_freq const &y) {
  return {x.n + y.n + (x.statistic & y.statistic), x.beta, ((x.statistic ^ y.statistic) == 1 ? Fermion : Boson)};
 }

 inline matsubara_freq operator-(matsubara_freq const &x, matsubara_freq const &y) {
  return {x.n - y.n - (~x.statistic & y.statistic), x.beta, ((x.statistic ^ y.statistic) == 1 ? Fermion : Boson)};
 }

 inline matsubara_freq operator-(matsubara_freq const &mp) {
  return {-(mp.n + (mp.statistic == Fermion ? 1 : 0)), mp.beta, mp.statistic};
 }

 //---------------------------------------------------------------------------------------------------------
 /// The domain
 template <bool IsFreq> struct matsubara_domain {
  using point_t = typename std::conditional<IsFreq, std::complex<double>, double>::type;
  double beta;
  statistic_enum statistic;
  matsubara_domain(double beta, statistic_enum s) : beta(beta), statistic(s) {
   if (beta < 0) TRIQS_RUNTIME_ERROR << "Matsubara domain construction :  beta <0 : beta =" << beta << "\n";
  }
  matsubara_domain() : matsubara_domain(1, Fermion) {}
  matsubara_domain(matsubara_domain const &) = default;
  matsubara_domain(matsubara_domain<!IsFreq> const &x) : matsubara_domain(x.beta, x.statistic) {}
  bool operator==(matsubara_domain const &D) const { return ((std::abs(beta - D.beta) < 1.e-15) && (statistic == D.statistic)); }

  /// Write into HDF5
  friend void h5_write(h5::group fg, std::string subgroup_name, matsubara_domain const &d) {
   h5::group gr = fg.create_group(subgroup_name);
   h5_write(gr, "beta", d.beta);
   h5_write(gr, "statistic", (d.statistic == Fermion ? "F" : "B"));
  }

  /// Read from HDF5
  friend void h5_read(h5::group fg, std::string subgroup_name, matsubara_domain &d) {
   h5::group gr = fg.open_group(subgroup_name);
   double beta;
   std::string statistic;
   h5_read(gr, "beta", beta);
   h5_read(gr, "statistic", statistic);
   d = matsubara_domain(beta, (statistic == "F" ? Fermion : Boson));
  }

  //  BOOST Serialization
  friend class boost::serialization::access;
  template <class Archive> void serialize(Archive &ar, const unsigned int version) {
   ar &TRIQS_MAKE_NVP("beta", beta);
   ar &TRIQS_MAKE_NVP("statistic", statistic);
  }
 };

 using matsubara_freq_domain = matsubara_domain<true>;
 using matsubara_time_domain = matsubara_domain<false>;


 // ----- kronecker function : overload for matsubara_freq 
 inline bool kronecker(matsubara_freq const & freq) { return freq.n == 0; }
 inline bool kronecker(matsubara_freq const & f1, matsubara_freq const &f2) { return f1.n == f2.n; }
}
}