def main():
#
# create a system object with spin one-half sites and blocks.
#
spin_one_half_site = SpinOneHalfSite()
system = System(spin_one_half_site)
#
# build the Hamiltonian, and solve it using Lanczos.
#
set_hamiltonian_to_AF_Heisenberg(system)
ground_state_energy, ground_state_wf = system.calculate_ground_state()
#
# print results
#
print "The ground state energy is %8.6f." % ground_state_energy
print "The ground state wavefunction is :"
print ground_state_wf.as_matrix
def main(args):
#
# create a system object with spin one-half sites and blocks.
#
spin_one_half_site = SpinOneHalfSite()
system = System(spin_one_half_site)
#
# read command-line arguments and initialize some stuff
#
number_of_sites = int(args['-n'])
number_of_states_kept = int(args['-m'])
sizes = []
energies = []
entropies = []
truncation_errors = []
#
# infinite DMRG algorithm
#
number_of_sites = 2 * (number_of_sites / 2) # make it even
for current_size in range(4, number_of_sites + 1, 2):
#block_size = current_size / 2 - 1
energy, entropy, truncation_error = (infinite_dmrg_step(
system, current_size, number_of_states_kept))
sizes.append(current_size)
energies.append(energy)
entropies.append(entropy)
truncation_errors.append(truncation_error)
#
# save results
#
output_file = os.path.join(os.path.abspath(args['--dir']),
args['--output'])
f = open(output_file, 'w')
zipped = zip(sizes, energies, entropies, truncation_errors)
f.write('\n'.join('%s %s %s %s' % x for x in zipped))
f.close()
print 'Results stored in ' + output_file
def main(args):
#
# create a system object with electron sites and blocks, and set
# its model to be the Hubbard model.
#
electronic_site = ElectronicSite()
system = System(electronic_site)
system.model = HubbardModel()
#
# read command-line arguments and initialize some stuff
#
number_of_sites = int(args['-n'])
number_of_states_kept = int(args['-m'])
number_of_sweeps = int(args['-s'])
system.model.U = float(args['-U'])
number_of_states_infinite_algorithm = 10
if number_of_states_kept < number_of_states_infinite_algorithm:
number_of_states_kept = number_of_states_infinite_algorithm
sizes = []
energies = []
entropies = []
truncation_errors = []
system.number_of_sites = number_of_sites
#
# infinite DMRG algorithm
#
max_left_block_size = number_of_sites - 3
for left_block_size in range(1, max_left_block_size + 1):
energy, entropy, truncation_error = (system.infinite_dmrg_step(
left_block_size, number_of_states_infinite_algorithm))
current_size = left_block_size + 3
sizes.append(left_block_size)
energies.append(energy)
entropies.append(entropy)
truncation_errors.append(truncation_error)
#
# finite DMRG algorithm
#
states_to_keep = calculate_states_to_keep(
number_of_states_infinite_algorithm, number_of_states_kept,
number_of_sweeps)
half_sweep = 0
while half_sweep < len(states_to_keep):
# sweep to the left
for left_block_size in range(max_left_block_size, 0, -1):
states = states_to_keep[half_sweep]
energy, entropy, truncation_error = (system.finite_dmrg_step(
'right', left_block_size, states))
sizes.append(left_block_size)
energies.append(energy)
entropies.append(entropy)
truncation_errors.append(truncation_error)
half_sweep += 1
# sweep to the right
# if this is the last sweep, stop at the middle
if half_sweep == 2 * number_of_sweeps - 1:
max_left_block_size = number_of_sites / 2 - 1
for left_block_size in range(1, max_left_block_size + 1):
energy, entropy, truncation_error = (system.finite_dmrg_step(
'left', left_block_size, states))
sizes.append(left_block_size)
energies.append(energy)
entropies.append(entropy)
truncation_errors.append(truncation_error)
half_sweep += 1
#
# save results
#
output_file = os.path.join(os.path.abspath(args['--dir']),
args['--output'])
f = open(output_file, 'w')
zipped = zip(sizes, energies, entropies, truncation_errors)
f.write('\n'.join('%s %s %s %s' % x for x in zipped))
f.close()
print 'Results stored in ' + output_file