GroupedSite

class tenpy.networks.site.GroupedSite(sites, labels=None, charges='same')[source]

Bases: tenpy.networks.site.Site

Group two or more Site into a larger one.

A typical use-case is that you want a NearestNeighborModel for TEBD although you have next-nearest neighbor interactions: you just double your local Hilbertspace to consist of two original sites. Note that this is a ‘hack’ at the cost of other things (e.g., measurements of ‘local’ operators) getting more complicated/computationally expensive.

If the individual sites indicate fermionic operators (with entries in need_JW_string), we construct the new on-site oerators of site1 to include the JW string of site0, i.e., we use the Kronecker product of [JW, op] instead of [Id, op] if necessary (but always [op, Id]). In that way the onsite operators of this DoubleSite automatically fulfill the expected commutation relations. See also Fermions and the Jordan-Wigner transformation.

Parameters
siteslist of Site

The individual sites being grouped together. Copied before use if charges!='same'.

labels :

Include the Kronecker product of the each onsite operator op on sites[i] and identities on other sites with the name opname+labels[i]. Similarly, set state labels for ' '.join(state[i]+'_'+labels[i]). Defaults to [str(i) for i in range(n_sites)], which for example grouping two SpinSites gives operators name like "Sz0" and sites labels like 'up_0 down_1'.

charges'same' | 'drop' | 'independent'

How to handle charges, defaults to ‘same’. 'same' means that all sites have the same ChargeInfo, and the total charge is the sum of the charges on the individual sites. 'independent' means that the sites have possibly different ChargeInfo, and the charges are conserved separately, i.e., we have n_sites conserved charges. For 'drop', we drop any charges, such that the remaining legcharges are trivial.

Attributes
n_sitesint

The number of sites grouped together, i.e. len(sites).

siteslist of Site

The sites grouped together into self.

labels: list of str

The labels using which the single-site operators are added during construction.

Methods

add_op(self, name, op[, need_JW])

Add one on-site operators.

change_charge(self[, new_leg_charge, permute])

Change the charges of the site (in place).

get_op(self, name)

Return operator of given name.

kroneckerproduct(self, ops)

Return the Kronecker product \(op0 \otimes op1\) of local operators.

multiply_op_names(self, names)

Multiply operator names together.

op_needs_JW(self, name)

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

remove_op(self, name)

Remove an added operator.

rename_op(self, old_name, new_name)

Rename an added operator.

state_index(self, label)

Return index of a basis state from its label.

state_indices(self, labels)

Same as state_index(), but for multiple labels.

test_sanity(self)

Sanity check, raises ValueErrors, if something is wrong.

valid_opname(self, name)

Check whether ‘name’ labels a valid onsite-operator.
kroneckerproduct(self, ops)[source]

Return the Kronecker product \(op0 \otimes op1\) of local operators.

Parameters
opslist of Array

One operator (or operator name) on each of the ungrouped sites. Each operator should have labels ['p', 'p*'].

Returns
prodArray

Kronecker product \(ops[0] \otimes ops[1] \otimes \cdots\), with labels ['p', 'p*'].

add_op(self, name, op, need_JW=False)

Add one on-site operators.

Parameters
namestr

A valid python variable name, used to label the operator. The name under which op is added as attribute to self.

opnp.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_JWbool

Whether the operator needs a Jordan-Wigner string. If True, the function adds name to need_JW_string.

change_charge(self, new_leg_charge=None, permute=None)

Change the charges of the site (in place).

Parameters
new_leg_chargeLegCharge | None

The new charges to be used. If None, use trivial charges.

permutendarray | None

The permuation applied to the physical leg, which gets used to adjust state_labels and perm. If you sorted the previous leg with perm_qind, new_leg_charge = leg.sort(), use leg.perm_flat_from_perm_qind(perm_qind). Ignored if None.

property dim

Dimension of the local Hilbert space.

get_op(self, name)

Return operator of given name.

Parameters
namestr

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
opnp_conserved

The operator given by name, with labels 'p', 'p*'. If name already was an npc Array, it’s directly returned.

multiply_op_names(self, names)

Multiply operator names together.

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

Parameters
nameslist of str

List of valid operator labels.

Returns
combined_opnamestr

A valid operator name Operatorname representing the product of operators in names.

property onsite_ops

Dictionary of on-site operators for iteration.

Single operators are accessible as attributes.

op_needs_JW(self, name)

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

Parameters
namestr

The name of the operator, as in get_op().

Returns
needs_JWbool

Whether the operator needs a Jordan-Wigner string, judging from need_JW_string.

remove_op(self, name)

Remove an added operator.

Parameters
namestr

The name of the operator to be removed.

rename_op(self, old_name, new_name)

Rename an added operator.

Parameters
old_namestr

The old name of the operator.

new_namestr

The new name of the operator.

state_index(self, label)

Return index of a basis state from its label.

Parameters
labelint | string

eather the index directly or a label (string) set before.

Returns
state_indexint

the index of the basis state associated with the label.

state_indices(self, labels)

Same as state_index(), but for multiple labels.

test_sanity(self)

Sanity check, raises ValueErrors, if something is wrong.

valid_opname(self, name)

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

Parameters
namestr

Label for the operator. Can be multiple operator(labels) separated by whitespace, indicating that they should be multiplied together.

Returns
validbool

True if name is a valid argument to get_op().