lattice.cpp

/*
 * Copyright (c) 2013, Robert Rueger <rueger@itp.uni-frankfurt.de>
 *
 * This file is part of hVMC.
 *
 * hVMC 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.
 *
 * hVMC 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 hVMC.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "lattice.hpp"
using namespace std;


Lattice::index Lattice::get_index_from_spindex( Lattice::spindex l ) const
{
  assert( l < 2 * L );

  return l % L;

  // this is a branchless version of:
  // if ( get_spindex_type( l ) == Lattice::spindex_type::down ) {
  //   return l - L;
  // } else {
  //   return l;
  // }
}


Lattice::spindex Lattice::get_linked_spindex( Lattice::spindex l ) const
{
  assert( l < 2 * L );

  return l + ( 1 - static_cast<int>( 2 * ( l / L ) ) ) * L;

  // this is a branchless version of:
  // if ( get_spindex_type( l ) == Lattice::spindex_type::up ) {
  //   return l + L;
  // } else {
  //   return l - L;
  // }
}


Lattice::spindex_type Lattice::get_spindex_type( Lattice::spindex l ) const
{
  assert( l < 2 * L );

  if ( l < L ) {
    return Lattice::spindex_type::up;
  } else {
    return Lattice::spindex_type::down;
  }
}


vector<Lattice::spindex> Lattice::get_Xnn( Lattice::spindex l, unsigned int X ) const
{
  vector<Lattice::spindex> Xnn;
  get_Xnn( l, X, &Xnn );
  return Xnn;
}


Eigen::VectorXi Lattice::get_random_spindex_occ(
  unsigned int Npu, unsigned int Npd, mt19937& rng ) const
{
  // this is the default distribution if the lattice has no special needs:
  // it will just randomly distribute Npu/Npd particles per spin direction

  Eigen::VectorXi spindex_occ = Eigen::VectorXi::Zero( 2 * L );

  while ( spindex_occ.head( L ).sum() < static_cast<int>( Npu ) ) {
    spindex_occ[ uniform_int_distribution<Lattice::spindex>( 0, L - 1 )( rng ) ] = 1;
  }
  while ( spindex_occ.tail( L ).sum() < static_cast<int>( Npd ) ) {
    spindex_occ[ uniform_int_distribution<Lattice::spindex>( L, 2 * L - 1 )( rng ) ] = 1;
  }

  return spindex_occ;
}


bool Lattice::include_r_in_ssfac( index, index ) const
{
  return true;
}