def test_ascending_descending(chi, dtype):
"""
test if ascending and descending operations are doing the right thing
"""
wC, uC, rho_0 = bml.initialize_binary_MERA_random(phys_dim=2,
chi=chi,
dtype=dtype)
wC, uC = bml.unlock_layer(wC, uC) #add a transitional layer
wC, uC = bml.unlock_layer(wC, uC) #add a transitional layer
ham_0 = bml.initialize_TFI_hams(dtype)
rho = [0 for n in range(len(wC) + 1)]
ham = [0 for n in range(len(wC) + 1)]
rho[-1] = bml.steady_state_density_matrix(10, rho_0, wC[-1], uC[-1])
ham[0] = ham_0
for p in range(len(rho) - 2, -1, -1):
rho[p] = bml.descending_super_operator(rho[p + 1], wC[p], uC[p])
for p in range(len(wC)):
ham[p + 1] = bml.ascending_super_operator(ham[p], wC[p], uC[p])
energies = [
tn.ncon([rho[p], ham[p]], [[1, 2, 3, 4, 5, 6], [1, 2, 3, 4, 5, 6]])
for p in range(len(rho))
]
np.testing.assert_allclose(
np.array(
[energies[p] / energies[p + 1] for p in range(len(energies) - 1)]),
0.5)
def test_padding(chi, dtype):
wC, uC, rho_0 = bml.initialize_binary_MERA_random(phys_dim=2,
chi=chi,
dtype=dtype)
wC, uC = bml.unlock_layer(wC, uC) #add a transitional layer
wC, uC = bml.unlock_layer(wC, uC) #add a transitional layer
ham_0 = bml.initialize_TFI_hams(dtype)
def get_energies(wC, uC, rho_0, ham_0):
rho = [0 for n in range(len(wC) + 1)]
ham = [0 for n in range(len(wC) + 1)]
rho[-1] = bml.steady_state_density_matrix(10, rho_0, wC[-1], uC[-1])
ham[0] = ham_0
for p in range(len(rho) - 2, -1, -1):
rho[p] = bml.descending_super_operator(rho[p + 1], wC[p], uC[p])
for p in range(len(wC)):
ham[p + 1] = bml.ascending_super_operator(ham[p], wC[p], uC[p])
energies = [
tn.ncon([rho[p], ham[p]], [[1, 2, 3, 4, 5, 6], [1, 2, 3, 4, 5, 6]])
for p in range(len(rho))
]
return energies
energies_1 = get_energies(wC, uC, rho_0, ham_0)
chi_new = chi + 1
wC, uC = bml.pad_mera_tensors(chi_new, wC, uC)
rho_0 = misc_mera.pad_tensor(rho_0, [chi_new] * 6)
energies_2 = get_energies(wC, uC, rho_0, ham_0)
np.testing.assert_allclose(energies_1, energies_2)
def run_binary_mera_optimization_TFI(chis=[4, 6, 8],
niters=[200, 300, 1000],
embeddings=None,
dtype=tf.float64,
verbose=1,
nsteps_steady_state=4,
numpy_update=True,
opt_u_after=40,
opt_all_layers=None,
wC=0,
uC=0,
rho_0=0,
noises=None,
filename=None):
"""
optimize a binary mera to approximate the ground-state of the infinite transverse field Ising model
Args:
chis (list of int): bond dimension of successive MERA simulations
niters (list of int): number of optimization steps of successive MERA optimizations
embeddings (list of str or None): type of embedding scheme used to embed mera into the next larger bond dimension
entries can be: 'p' or 'pad' for padding with zeros without, if possible, adding new layers
'a' or 'add' for adding new layer with increased bond dimension
'n' for keeping the MERA as it is (e.g. for resuming optimization)
the first entry will be ignored for the case where no `wC` and `uC` tensors are passed
dtype (tensorflow dtype): dtype
verbose (int): verbosity flag, if `verbose>0`, print out info during optimization
nsteps_steady_state (int): number of power-method iteration steps for calculating the
steady state density matrices
numpy_update (bool): if True, use numpy svd to calculate update of disentanglers and isometries
opt_u_after (int): start optimizing disentangler only after `opt_u_after` initial optimization steps
opt_all_layers (bool): if `True`, optimize all layers
if `False`, only optimize truncating layers
wC (list of tf.Tensor or 0.0): initial values for isometries; if `0.0`, initialize with identities
uC (list of tf.Tensor or 0.0): initial values for disentanglers; if `0.0`, initialize with identities
rho_0 (tf.Tensor or 0.0): initial value for reduced density matrix; if `0.0`, initialize with identities
noises (list of float): noise values for initializing new layers
Returns:
wC (list of tf.Tensor): optimized isometries of the MERA
uC (list of tf.Tensor): optimized disentanglers of the MERA
energies (list of tf.Tensor): energies per iteration steps
walltimes (list of float): walltimes per iteration step
"""
if not embeddings:
embeddings = ['p'] * len(chis)
if not noises:
noises = [0.0] * len(chis)
if not opt_all_layers:
opt_all_layers = [True] * len(chis)
init = False
if wC == 0:
init = True
wC, _, _ = bml.initialize_binary_MERA_identities(phys_dim=2,
chi=chis[0],
dtype=dtype)
if uC == 0:
init = True
_, uC, _ = bml.initialize_binary_MERA_identities(phys_dim=2,
chi=chis[0],
dtype=dtype)
if rho_0 == 0:
_, _, rho_0 = bml.initialize_binary_MERA_identities(phys_dim=2,
chi=chis[0],
dtype=dtype)
ham_0 = bml.initialize_TFI_hams(dtype=dtype)
data = {'profile': {}, 'energies': {}}
for chi, niter, which, noise, opt_all in zip(chis, niters, embeddings,
noises, opt_all_layers):
energies = []
walltimes = []
if not init:
if which in ('a', 'add'):
wC, uC = bml.unlock_layer(wC, uC, noise=noise)
wC, uC = bml.pad_mera_tensors(chi, wC, uC, noise=noise)
elif which in ('p', 'pad'):
wC, uC = bml.pad_mera_tensors(chi, wC, uC, noise=noise)
rho_0 = misc_mera.pad_tensor(rho_0, [chi, chi, chi, chi, chi, chi])
wC, uC, rho_0, times, es = bml.optimize_binary_mera(
ham_0=ham_0,
#rho_0=rho_0,
wC=wC,
uC=uC,
numiter=niter,
nsteps_steady_state=nsteps_steady_state,
verbose=verbose,
opt_u=True,
opt_w=True,
numpy_update=numpy_update,
opt_u_after=opt_u_after,
opt_all_layers=opt_all)
energies.extend(es)
walltimes.extend(times)
data['profile'][chi] = walltimes
data['energies'][chi] = energies
init = False
if filename:
with open(filename + '_tensors.pickle', 'wb') as f:
pickle.dump([wC, uC], f)
with open('energies_walltimes_' + filename + '.pickle', 'wb') as f:
pickle.dump(data, f)
return wC, uC, walltimes, energies