Site¶

full name: tenpy.networks.site.Site
parent module: tenpy.networks.site
type: class

Inheritance Diagram

Methods

`Site.__init__`(leg[, state_labels, sort_charge])
`Site.add_op`(name, op[, need_JW, hc, ...])	Add one on-site operators.
`Site.change_charge`([new_leg_charge, permute])	Change the charges of the site (in place).
`Site.from_hdf5`(hdf5_loader, h5gr, subpath)	Load instance from a HDF5 file.
`Site.get_hc_op_name`(name)	Return the hermitian conjugate of a given operator.
`Site.get_op`(name)	Return operator of given name.
`Site.multiply_op_names`(names)	Multiply operator names together.
`Site.multiply_operators`(operators)	Multiply local operators (possibly given by their names) together.
`Site.op_needs_JW`(name)	Whether an (composite) onsite operator is fermionic and needs a Jordan-Wigner string.
`Site.remove_op`(name)	Remove an added operator.
`Site.rename_op`(old_name, new_name)	Rename an added operator.
`Site.save_hdf5`(hdf5_saver, h5gr, subpath)	Export self into a HDF5 file.
`Site.sort_charge`([bunch])	Sort the `leg` charges (in place).
`Site.state_index`(label)	Return index of a basis state from its label.
`Site.state_indices`(labels)	Same as `state_index()`, but for multiple labels.
`Site.test_sanity`()	Sanity check, raises ValueErrors, if something is wrong.
`Site.valid_opname`(name)	Check whether 'name' labels a valid onsite-operator.

Class Attributes and Properties

`Site.dim`	Dimension of the local Hilbert space.
`Site.onsite_ops`	Dictionary of on-site operators for iteration.

class tenpy.networks.site.Site(leg, state_labels=None, sort_charge=False, **site_ops)[source]¶

Bases: Hdf5Exportable

Collects necessary information about a single local site of a lattice.

This class defines what the local basis states are: it provides the leg defining the charges of the physical leg for this site. Moreover, it stores (local) on-site operators, which are directly available as attribute, e.g., self.Sz is the Sz operator for the SpinSite. Alternatively, operators can be obtained with get_op(). The operator names Id and JW are reserved for the identity and Jordan-Wigner strings.

Warning

The order of the local basis can change depending on the charge conservation! This is a necessary feature since we need to sort the basis by charges for efficiency. We use the state_labels and perm to keep track of these permutations.

Changed in version 0.10: Add the option sort_charge. Right now the default behavriou is False for backwards compatibility, but we will change it for Version 1.0 to True. For now, we raise a warning in cases where it can lead to changes. If you see this warning, just set the value explicitly to avoid breaking compatibility of existing data with future releases. Set it to False, if you already have data (for your particular model), that you want to be able to load/compare to. If you start a new project and don’t have data yet, set it to True. See also the breaking changes section in the release notes.

Parameters

leg (LegCharge) – Charges of the physical states, to be used for the physical leg of MPS.
state_labels (None | list of str) – Optionally a label for each local basis states. None entries are ignored / not set.
**site_ops – Additional keyword arguments of the form name=op given to add_op(). The identity operator 'Id' is automatically included. If no 'JW' for the Jordan-Wigner string is given, 'JW' is set as an alias to 'Id'.
sort_charge (bool | None) – Whether sort_charge() should be called at the end of initialization. This is usually a good idea to reduce potential overhead when using charge conservation. Note that this might permute the order of the local basis states! For backwards compatibility with existing data, it is not (yet) enabled by default, but we started to warn about the behaviour. Explicitly set sort_charge=False to disable the warning.

leg¶

Charges of the local basis states.

Type: LegCharge

state_labels¶

(Optional) labels for the local basis states.

Type: {str: int}

opnames¶

Labels of all onsite operators (i.e. self.op exists if 'op' in self.opnames). Note that get_op() allows arbitrary concatenations of them.

Type: set

need_JW_string¶

Labels of all onsite operators that need a Jordan-Wigner string. Used in op_needs_JW() to determine whether an operator anticommutes or commutes with operators on other sites.

Type: set

ops¶

Onsite operators are added directly as attributes to self. For example after self.add_op('Sz', Sz) you can use self.Sz for the Sz operator. All onsite operators have labels 'p', 'p*'.

Type: Array

perm¶

Index permutation of the physical leg compared to conserve=None, i.e. OP_conserved = OP_nonconserved[np.ix_(perm,perm)] and perm[state_labels_conserved["some_state"]] == state_labels_nonconserved["some_state"].

Type: 1D array

JW_exponent¶

Exponents of the 'JW' operator, such that self.JW.to_ndarray() = np.diag(np.exp(1.j*np.pi* JW_exponent))

Type: 1D array

hc_ops¶

Mapping from operator names to their hermitian conjugates. Use get_hc_op_name() to obtain entries.

Type: dict(str->str)

used_sort_charge¶

Whether sort_charge() was called. Note that the default argument for sort_dense in add_op() changes to True in that case, to ensure a consistent use.

Type: bool

Examples

The following generates a site for spin-1/2 with Sz conservation. Note that Sx = (Sp + Sm)/2 violates Sz conservation and is thus not a valid on-site operator.

>>> chinfo = npc.ChargeInfo([1], ['2*Sz'])
>>> ch = npc.LegCharge.from_qflat(chinfo, [1, -1])
>>> Sp = [[0, 1.], [0, 0]]
>>> Sm = [[0, 0], [1., 0]]
>>> Sz = [[0.5, 0], [0, -0.5]]
>>> site = tenpy.networks.site.Site(ch, ['up', 'down'], Splus=Sp, Sminus=Sm, Sz=Sz)
>>> print(site.Splus.to_ndarray())
[[0. 1.]
 [0. 0.]]
>>> print(site.get_op('Sminus').to_ndarray())
[[0. 0.]
 [1. 0.]]
>>> print(site.get_op('Splus Sminus').to_ndarray())
[[1. 0.]
 [0. 0.]]

change_charge(new_leg_charge=None, permute=None)[source]¶

Change the charges of the site (in place).

Parameters

new_leg_charge (LegCharge | None) – The new charges to be used. If None, use trivial charges.
permute (ndarray | None) – The permuation applied to the physical leg, which also gets used to adjust state_labels and perm. If you sorted the previous leg with perm_qind, new_leg_charge = leg.sort(), use old_leg.perm_flat_from_perm_qind(perm_qind). Ignored if None.

sort_charge(bunch=True)[source]¶

Sort the leg charges (in place).

Parameters: bunch (bool) – Whether to also group equal charges into larger blocks (usually a good idea).
Returns: perm – The permutation
Return type: 1D ndarray

test_sanity()[source]¶: Sanity check, raises ValueErrors, if something is wrong.

property dim¶: Dimension of the local Hilbert space.

property onsite_ops¶

Dictionary of on-site operators for iteration.

Single operators are accessible as attributes.

add_op(name, op, need_JW=False, hc=None, permute_dense=None)[source]¶

Add one on-site operators.

Parameters

name (str) – A valid python variable name, used to label the operator. The name under which op is added as attribute to self.
op (np.ndarray | Array) – A matrix acting on the local hilbert space representing the local operator. Dense numpy arrays are automatically converted to Array. LegCharges have to be [leg, leg.conj()]. We set labels 'p', 'p*'.
need_JW (bool) – Whether the operator needs a Jordan-Wigner string. If True, add name to need_JW_string.
hc (None | False | str) – The name for the hermitian conjugate operator, to be used for hc_ops. By default (None), try to auto-determine it. If False, disable adding antries to hc_ops.
permute_dense (bool | None) – Flag to enable/disable permuations when converting op from numpy to np_conserved arrays. If True, the operator is permuted with perm to account for permutations induced by sorting charges; False disables the permutations. By default (None), the value of used_sort_charge is used.

rename_op(old_name, new_name)[source]¶

Rename an added operator.

Parameters

old_name (str) – The old name of the operator.
new_name (str) – The new name of the operator.

remove_op(name)[source]¶

Remove an added operator.

Parameters: name (str) – The name of the operator to be removed.

state_index(label)[source]¶

Return index of a basis state from its label.

Parameters: label (int | string) – eather the index directly or a label (string) set before.
Returns: state_index – the index of the basis state associated with the label.
Return type: int

state_indices(labels)[source]¶: Same as state_index(), but for multiple labels.

get_op(name)[source]¶

Return operator of given name.

Parameters: name (str) – The name of the operator to be returned. In case of multiple operator names separated by whitespace, we multiply them together to a single on-site operator (with the one on the right acting first).
Returns: op – The operator given by name, with labels 'p', 'p*'. If name already was an npc Array, it’s directly returned.
Return type: np_conserved

get_hc_op_name(name)[source]¶

Return the hermitian conjugate of a given operator.

Parameters: name (str) – The name of the operator to be returned. Multiple operators separated by whitespace are interpreted as an operator product, exactly as get_op() does.
Returns: hc_op_name – Operator name for the hermi such that get_op() of
Return type: str

op_needs_JW(name)[source]¶

Whether an (composite) onsite operator is fermionic and needs a Jordan-Wigner string.

Parameters: name (str) – The name of the operator, as in get_op().
Returns: needs_JW – Whether the operator needs a Jordan-Wigner string, judging from need_JW_string.
Return type: bool

valid_opname(name)[source]¶

Check whether ‘name’ labels a valid onsite-operator.

Parameters: name (str) – Label for the operator. Can be multiple operator(labels) separated by whitespace, indicating that they should be multiplied together.
Returns: valid – True if name is a valid argument to get_op().
Return type: bool

multiply_op_names(names)[source]¶

Multiply operator names together.

Join the operator names in names such that get_op returns the product of the corresponding operators.

Parameters: names (list of str) – List of valid operator labels.
Returns: combined_opname – A valid operator name Operatorname representing the product of operators in names.
Return type: str

multiply_operators(operators)[source]¶

Multiply local operators (possibly given by their names) together.

Parameters: operators (list of {str | Array}) – List of valid operator names (to be translated with get_op()) or directly on-site operators in the form of npc arrays with 'p', 'p*' label. The operators are multiplied left-to-right.
Returns: combined_operator – The product of the given operators in a left-to-right multiplication following the usual mathematical convention. For example, if operators=['Sz', 'Sp', 'Sx'], the final operator is equivalent to site.get_op('Sz Sp Sx'), with the 'Sx' operator acting first on any physical state.
Return type: Array

classmethod from_hdf5(hdf5_loader, h5gr, subpath)[source]¶

Load instance from a HDF5 file.

This method reconstructs a class instance from the data saved with save_hdf5().

Parameters

hdf5_loader (Hdf5Loader) – Instance of the loading engine.
h5gr (Group) – HDF5 group which is represent the object to be constructed.
subpath (str) – The name of h5gr with a '/' in the end.

Returns

obj – Newly generated class instance containing the required data.

Return type

cls

save_hdf5(hdf5_saver, h5gr, subpath)[source]¶

Export self into a HDF5 file.

This method saves all the data it needs to reconstruct self with from_hdf5().

This implementation saves the content of __dict__ with save_dict_content(), storing the format under the attribute 'format'.

Parameters

hdf5_saver (Hdf5Saver) – Instance of the saving engine.
h5gr (:class`Group`) – HDF5 group which is supposed to represent self.
subpath (str) – The name of h5gr with a '/' in the end.