phase_t Lattice::enforce_boundary (LatticeSite &site, const BoundaryConditions &bcs) const
{
BOOST_ASSERT(site.n_dimensions() == n_dimensions());
BOOST_ASSERT(bcs.size() == 0 || bcs.size() == n_dimensions());
phase_t phase_change = 1;
for (unsigned int dim = 0; dim < n_dimensions(); ++dim) {
while (site[dim] >= dimensions[dim]) {
site[dim] -= dimensions[dim];
if (bcs.size() != 0)
phase_change *= bcs[dim].phase();
}
while (site[dim] < 0) {
site[dim] += dimensions[dim];
if (bcs.size() != 0)
phase_change *= std::conj(bcs[dim].phase());
}
}
// this is often unnecessary ... should it be in a separate
// function to be called before this one when needed?
do_safe_modulus(site.basis_index, basis_indices);
BOOST_ASSERT(site_is_valid(site));
return phase_change;
}
AmplitudeType BasicOperatorEvaluator::evaluate (const typename Wavefunction<AmplitudeType>::Amplitude &wfa, const BoundaryConditions<AmplitudeType> &bcs) const
{
typedef AmplitudeType PhaseType;
assert(&wfa.get_lattice() == m_operator.lattice.get());
assert(wfa.get_positions().get_N_species() >= min_required_species);
const PositionArguments &r = wfa.get_positions();
const Lattice &lattice = wfa.get_lattice();
const bool is_sum_over_sites = (bcs.size() != 0);
AmplitudeType meas = 0;
const Big<AmplitudeType> old_psi(wfa.psi());
// we only iterate if doing a sum, and even then we only want to iterate
// over BraivaisSite's
const unsigned int n_iterations = is_sum_over_sites ? lattice.total_sites() / lattice.basis_indices : 1;
// FIXME: need a faster way of iterating the lattice
for (unsigned int i = 0; i < n_iterations; ++i) {
const LatticeSite site_offset(lattice[i]);
// we only want to iterate over BravaisSite's
assert(site_offset.basis_index == 0);
PhaseType phase = 1;
Move move;
for (unsigned int j = 0; j < m_operator.hopv.size(); ++j) {
PhaseType srcphase;
const unsigned int species = m_operator.hopv[j].get_species();
LatticeSite src(m_operator.hopv[j].get_source());
lattice.asm_add_site_vector(src, site_offset.bravais_site());
assert(is_sum_over_sites || lattice.site_is_valid(src));
srcphase = lattice.enforce_boundary(src, bcs);
if (srcphase == PhaseType(0))
goto current_measurement_is_zero;
const int particle_index = r.particle_index_at_position(lattice.index(src), species);
if (particle_index < 0)
goto current_measurement_is_zero;
if (m_operator.hopv[j].get_source() != m_operator.hopv[j].get_destination()) {
LatticeSite dest(m_operator.hopv[j].get_destination());
lattice.asm_add_site_vector(dest, site_offset.bravais_site());
assert(is_sum_over_sites || lattice.site_is_valid(dest));
phase *= lattice.enforce_boundary(dest, bcs) / srcphase;
if (phase == PhaseType(0))
goto current_measurement_is_zero;
const unsigned int dest_index = lattice.index(dest);
if (r.is_occupied(dest_index, species))
goto current_measurement_is_zero;
move.push_back(SingleParticleMove(Particle(particle_index, species), dest_index));
}
}
// now perform the move (if necessary)
if (move.size() != 0) {
BasicOperatorEvaluatorLocal::TemporaryMove<AmplitudeType> temp_move(wfa, move);
// fixme: check logic of multiplying by phase (c.f. above), as
// well as logic of source and destination
meas += vmc_conj(phase * wfa.psi().ratio(old_psi));
} else {
meas += 1;
}
current_measurement_is_zero: ;
}
return meas;
}