dft_tools/triqs/gf/local/fourier_matsubara.cpp

/*******************************************************************************
 * 
 * TRIQS: a Toolbox for Research in Interacting Quantum Systems
 *
 * Copyright (C) 2011 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/>.
 *
 ******************************************************************************/

#include "fourier_matsubara.hpp"
#include <fftw3.h>

namespace triqs { namespace gf { 
 
 namespace impl_local_matsubara {
  
  inline dcomplex oneFermion(dcomplex a,double b,double tau,double beta) {
   return -a*( b >=0 ? exp(-b*tau)/(1+exp(-beta*b)) : exp(b*(beta-tau))/(1+exp(beta*b)) );
  }
  
  inline dcomplex oneBoson(dcomplex a,double b,double tau,double beta) {
   return a*( b >=0 ? exp(-b*tau)/(exp(-beta*b)-1) : exp(b*(beta-tau))/(1-exp(b*beta)) );
  }
 }
 
 template<typename GfElementType> GfElementType convert_green         ( dcomplex const& x) { return x;}
 template<>                       double        convert_green<double> ( dcomplex const& x) { return real(x);}
 
 //--------------------------------------------------------------------------------------
 
 struct impl_worker {
  
  tqa::vector<dcomplex> g_in, g_out;
  
  void direct ( gf_view<imfreq,scalar_valued> &gw , gf_view<imtime,scalar_valued> const& gt) {
   using namespace impl_local_matsubara;
   auto ta = gt(freq_infty());
   //TO BE MODIFIED AFTER SCALAR IMPLEMENTATION TODO
   dcomplex d= ta(1)(0,0), A= ta.get_or_zero(2)(0,0), B = ta.get_or_zero(3)(0,0);
   double b1=0, b2=0, b3=0;
   dcomplex a1, a2, a3;
   double beta=gt.mesh().domain().beta;
   auto L = ( gt.mesh().kind() == full_bins ? gt.mesh().size()-1 : gt.mesh().size());
   double fact= beta/ gt.mesh().size();
   dcomplex iomega = dcomplex(0.0,1.0) * std::acos(-1) / beta;
   dcomplex iomega2 = iomega * 2 * gt.mesh().delta() * ( gt.mesh().kind() == half_bins ? 0.5 : 0.0);
   g_in.resize(gt.mesh().size());
   g_out.resize(gw.mesh().size());
   if (gw.domain().statistic == Fermion){
    b1 = 0; b2 =1; b3 =-1; 
    a1 = d-B; a2 = (A+B)/2; a3 = (B-A)/2; 
   }
   else { 
    b1 = -0.5; b2 =-1; b3 =1; 
    a1 = 4*(d-B)/3; a2 = B-(d+A)/2; a3 = d/6+A/2+B/3; 
   }
   if (gw.domain().statistic == Fermion){
    for (auto & t : gt.mesh())  
     g_in(t.index()) = fact * exp(iomega*t) * ( gt(t) - ( oneFermion(a1,b1,t,beta) + oneFermion(a2,b2,t,beta)+ oneFermion(a3,b3,t,beta) ) );
   }
   else {
    for (auto & t : gt.mesh()) 
     g_in(t.index()) =  fact * ( gt(t) -  ( oneBoson(a1,b1,t,beta) + oneBoson(a2,b2,t,beta) + oneBoson(a3,b3,t,beta) ) );  
   }
   details::fourier_base(g_in, g_out, L, true);
   for (auto & w : gw.mesh()) {
    gw(w) = g_out( w.index() ) * exp(iomega2*w.index() ) + a1/(w-b1) + a2/(w-b2) + a3/(w-b3); 
   }
   gw.singularity() = gt.singularity();// set tail
  }
  
  
  
  void inverse(gf_view<imtime,scalar_valued> gt, gf_view<imfreq,scalar_valued> const gw){
   using namespace impl_local_matsubara;
   static bool Green_Function_Are_Complex_in_time = false;
   // If the Green function are NOT complex, then one use the symmetry property
   // fold the sum and get a factor 2
   auto ta = gw(freq_infty());
   //TO BE MODIFIED AFTER SCALAR IMPLEMENTATION TODO
   dcomplex d= ta(1)(0,0), A= ta.get_or_zero(2)(0,0), B = ta.get_or_zero(3)(0,0);
   double b1, b2, b3;
   dcomplex a1, a2, a3;
   
   double beta=gw.domain().beta;
   size_t L= gt.mesh().size() - ( gt.mesh().kind() == full_bins ? 1 : 0); //L can be different from gt.mesh().size() (depending on the mesh kind) and is given to the FFT algorithm 
   dcomplex iomega = dcomplex(0.0,1.0) * std::acos(-1) / beta;
   dcomplex iomega2 = -iomega * 2 * gt.mesh().delta() * (gt.mesh().kind() == half_bins ? 0.5 : 0.0) ; 
   double fact = (Green_Function_Are_Complex_in_time ? 1 : 2)/beta;
   g_in.resize( gw.mesh().size());
   g_out.resize(gt.mesh().size());
   
   if (gw.domain().statistic == Fermion){
    b1 = 0; b2 =1; b3 =-1; 
    a1 = d-B; a2 = (A+B)/2; a3 = (B-A)/2; 
   }
   else { 
    b1 = -0.5; b2 =-1; b3 =1; 
    a1=4*(d-B)/3; a2=B-(d+A)/2; a3=d/6+A/2+B/3;
   }
   g_in() = 0;
   for (auto & w: gw.mesh()) {
    g_in( w.index() ) =  fact * exp(w.index()*iomega2) * ( gw(w) - (a1/(w-b1) + a2/(w-b2) + a3/(w-b3)) );
   }
   // for bosons GF(w=0) is divided by 2 to avoid counting it twice
   if (gw.domain().statistic == Boson && !Green_Function_Are_Complex_in_time ) g_in(0) *= 0.5;
   
   details::fourier_base(g_in, g_out, L, false);
   
   // CORRECT FOR COMPLEX G(tau) !!!
   typedef double gt_result_type;
   //typedef typename gf<imtime>::mesh_type::gf_result_type gt_result_type;
   if (gw.domain().statistic == Fermion){
    for (auto & t : gt.mesh()){
     gt(t) = convert_green<gt_result_type> ( g_out( t.index() == L ? 0 : t.index() ) * exp(-iomega*t)
     + oneFermion(a1,b1,t,beta) + oneFermion(a2,b2,t,beta)+ oneFermion(a3,b3,t,beta) );
    }
   }
   else {
    for (auto & t : gt.mesh()) 
     gt(t) = convert_green<gt_result_type> ( g_out( t.index() == L ? 0 : t.index() )
     + oneBoson(a1,b1,t,beta) + oneBoson(a2,b2,t,beta) + oneBoson(a3,b3,t,beta) );
   }
   if (gt.mesh().kind() == full_bins)
    gt.on_mesh(L) = -gt.on_mesh(0)-convert_green<gt_result_type>(ta(1)(0,0));
   // set tail
    gt.singularity() = gw.singularity();
  }
  
 };
 
 void fourier_impl  (gf_view<imfreq,scalar_valued> gw , gf_view<imtime,scalar_valued> const gt, scalar_valued){
  impl_worker w;
  w.direct(gw,gt);
 }
 
 void fourier_impl  (gf_view<imfreq,matrix_valued> gw , gf_view<imtime,matrix_valued> const gt, matrix_valued){
  impl_worker w;
  for (size_t n1=0; n1<gt.data().shape()[1];n1++)
   for (size_t n2=0; n2<gt.data().shape()[2];n2++){
    auto gw_sl=slice_target_to_scalar(gw,n1,n2);
    auto gt_sl=slice_target_to_scalar(gt,n1,n2);
    w.direct(gw_sl, gt_sl);
   }
 }
 
 
 
 //---------------------------------------------------------------------------
 
 void inverse_fourier_impl  (gf_view<imtime,scalar_valued> gt , gf_view<imfreq,scalar_valued> const gw, scalar_valued){ 
  impl_worker w;
  w.inverse(gt,gw);
 }
 
 void inverse_fourier_impl  (gf_view<imtime,matrix_valued> gt , gf_view<imfreq,matrix_valued> const gw, matrix_valued){
  impl_worker w;
  for (size_t n1=0; n1<gw.data().shape()[1];n1++)
   for (size_t n2=0; n2<gw.data().shape()[2];n2++){
    auto gt_sl=slice_target_to_scalar(gt, n1, n2);
    auto gw_sl=slice_target_to_scalar(gw, n1, n2);
    w.inverse( gt_sl, gw_sl);
   }
 }
 
 
 
 //---------------------------------------------------------------------------
 void triqs_gf_view_assign_delegation( gf_view<imfreq,scalar_valued> g, gf_keeper<tags::fourier,imtime,scalar_valued> const & L) { fourier_impl ( g ,L.g, scalar_valued() ); }
 void triqs_gf_view_assign_delegation( gf_view<imfreq,matrix_valued> g, gf_keeper<tags::fourier,imtime,matrix_valued> const & L) { fourier_impl ( g, L.g, matrix_valued() ); }
 void triqs_gf_view_assign_delegation( gf_view<imtime,scalar_valued> g, gf_keeper<tags::fourier,imfreq,scalar_valued> const & L) { inverse_fourier_impl( g, L.g, scalar_valued() ); }
 void triqs_gf_view_assign_delegation( gf_view<imtime,matrix_valued> g, gf_keeper<tags::fourier,imfreq,matrix_valued> const & L) { inverse_fourier_impl( g, L.g, matrix_valued() ); }
 
}}