Sweep¶
full name: tenpy.algorithms.mps_sweeps.Sweep
parent module:
tenpy.algorithms.mps_sweeps
type: class
Inheritance Diagram
Methods

Initialize self. 

Perform N_sweeps sweeps without optimization to update the environment. 
Define the schedule of the sweep. 


(Re)initialize the environment. 
Set self.mixer to the class specified by engine_params[‘mixer’]. 

Cleanup the effects of a mixer. 


Algorithmspecific actions to be taken after local update. 
Prepare everything algorithmspecific to perform a local update. 

Reset the statistics. 


One ‘sweep’ of a sweeper algorithm. 

Perform algorithmspecific local update. 

class
tenpy.algorithms.mps_sweeps.
Sweep
(psi, model, engine_params)[source]¶ Bases:
object
Prototype class for a ‘sweeping’ algorithm.
This is a superclass, intended to cover common procedures in all algorithms that ‘sweep’. This includes DMRG, TDVP, TEBD, etc. Only DMRG is currently implemented in this way.
 Parameters
psi (
MPS
) – Initial guess for the ground state, which is to be optimized inplace.model (
MPOModel
) – The model representing the Hamiltonian for which we want to find the ground state.engine_params (dict) – Further optional parameters. These are usually algorithmspecific, and thus should be described in subclasses.

chi_list
¶ A dictionary to gradually increase the chi_max parameter of trunc_params. The key defines starting from which sweep chi_max is set to the value, e.g.
{0: 50, 20: 100}
useschi_max=50
for the first 20 sweeps andchi_max=100
afterwards. Overwrites trunc_params[‘chi_list’]`. By default (None
) this feature is disabled. Type
dict 
None

combine
¶ Whether to combine legs into pipes as far as possible. This reduces the overhead of calculating charge combinations in the contractions. Makes the twosite DMRG engine equivalent to the old EngineCombine.
 Type

env
¶ Environment for contraction
<psiHpsi>
. Type

i0
¶ Only set during sweep. Leftmost of the EffectiveH.length sites to be updated in
update_local()
. Type

mixer
¶ If
None
, no mixer is used (anymore), otherwise the mixer instance. Type
Mixer
None

move_right
¶ Only set during sweep. Whether the next i0 of the sweep will be right or left of the current one.
 Type

ortho_to_envs
¶ List of environments
<psipsi_ortho>
, where psi_ortho is an MPS to orthogonalize against. Type
list of
MPSEnvironment

shelve
¶ If a simulation runs out of time (time.time()  start_time > max_seconds), the run will terminate with shelve = True.
 Type

update_LP_RP
¶ Only set during a sweep. Whether it is necessary to update the LP and RP. The latter are chosen such that the environment is growing for infinite systems, but we only keep the minimal number of environment tensors in memory (inside
env
).

verbose
¶ Level of verbosity (i.e. how much status information to print); higher=more output.
 Type
bool  int

init_env
(model=None)[source]¶ (Re)initialize the environment.
This function is useful to (re)start a Sweep with a slightly different model or different (engine) parameters. Note that we assume that we still have the same psi. Calls
reset_stats()
. Parameters
model (
MPOModel
) – The model representing the Hamiltonian for which we want to find the ground state. IfNone
, keep the model used before. Raises
ValueError – If the engine is reinitialized with a new model, which legs are incompatible with those of hte old model.

reset_stats
()[source]¶ Reset the statistics. Useful if you want to start a new Sweep run.
This method is expected to be overwritten by subclass, and should then define self.update_stats and self.sweep_stats dicts consistent with the statistics generated by the algorithm particular to that subclass.

environment_sweeps
(N_sweeps)[source]¶ Perform N_sweeps sweeps without optimization to update the environment.
 Parameters
N_sweeps (int) – Number of sweeps to run without optimization

sweep
(optimize=True, meas_E_trunc=False)[source]¶ One ‘sweep’ of a sweeper algorithm.
Iteratate over the bond which is optimized, to the right and then back to the left to the starting point. If optimize=False, don’t actually diagonalize the effective hamiltonian, but only update the environment.
 Parameters
 Returns
max_trunc_err (float) – Maximal truncation error introduced.
max_E_trunc (
None
 float) –None
if meas_E_trunc is False, else the maximal change of the energy due to the truncation.

get_sweep_schedule
()[source]¶ Define the schedule of the sweep.
One ‘sweep’ is a full sequence from the leftmost site to the right and back. Only those LP and RP that can be used later should be updated.
 Returns
schedule – Schedule for the sweep. Each entry is
(i0, move_right, (update_LP, update_RP))
, where i0 is the leftmost of theself.EffectiveH.length
sites to be updated inupdate_local()
, move_right indicates whether the next i0 in the schedule is rigth (True) of the current one, and update_LP, update_RP indicate whether it is necessary to update the LP and RP. The latter are chosen such that the environment is growing for infinite systems, but we only keep the minimal number of environment tensors in memory. Return type

mixer_cleanup
()[source]¶ Cleanup the effects of a mixer.
A
sweep()
with an enabledMixer
leaves the MPS psi with 2D arrays in S. To recover the originial form, this function simply performs one sweep with disabled mixer.