# CouplingTerms¶

Inheritance Diagram

Methods

 CouplingTerms.__init__(L) Initialize self. CouplingTerms.add_coupling_term(strength, i, …) Add a two-site coupling term on given MPS sites. Add terms from coupling_terms to an MPOGraph. Helping function to call before add_multi_coupling_term(). CouplingTerms.from_hdf5(hdf5_loader, h5gr, …) Load instance from a HDF5 file. Determine the maximal range in coupling_terms. CouplingTerms.plot_coupling_terms(ax, lat[, …]) “Plot coupling terms into a given lattice. CouplingTerms.remove_zeros([tol_zero]) Remove entries close to 0 from coupling_terms. CouplingTerms.save_hdf5(hdf5_saver, h5gr, …) Export self into a HDF5 file. Convert onsite_terms into a TermList. Convert the coupling_terms into Arrays on nearest neighbor bonds.
class tenpy.networks.terms.CouplingTerms(L)[source]

Operator names, site indices and strengths representing two-site coupling terms.

Parameters

L (int) – Number of sites.

L

Number of sites.

Type

int

coupling_terms

Filled by add_coupling_term(). Nested dictionaries of the form {i: {('opname_i', 'opname_string'): {j: {'opname_j': strength}}}}. Note that always i < j, but entries with j >= L are allowed for bc_MPS == 'infinite', in which case they indicate couplings between different iMPS unit cells.

Type

dict of dict

max_range()[source]

Determine the maximal range in coupling_terms.

Returns

max_range – The maximum of j - i for the i, j occuring in a term of coupling_terms.

Return type

int

add_coupling_term(strength, i, j, op_i, op_j, op_string='Id')[source]

Add a two-site coupling term on given MPS sites.

Parameters
• strength (float) – The strength of the coupling term.

• i (int) – The MPS indices of the two sites on which the operator acts. We require 0 <= i < N_sites and i < j, i.e., op_i acts “left” of op_j. If j >= N_sites, it indicates couplings between unit cells of an infinite MPS.

• j (int) – The MPS indices of the two sites on which the operator acts. We require 0 <= i < N_sites and i < j, i.e., op_i acts “left” of op_j. If j >= N_sites, it indicates couplings between unit cells of an infinite MPS.

• op1 (str) – Names of the involved operators.

• op2 (str) – Names of the involved operators.

• op_string (str) – The operator to be inserted between i and j.

coupling_term_handle_JW(strength, term, sites, op_string=None)[source]

Helping function to call before add_multi_coupling_term().

Parameters
• strength (float) – The strength of the coupling term.

• term ([(str, int), (str, int)]) – List of two tuples (op, i) where i is the MPS index of the site the operator named op acts on.

• sites (list of Site) – Defines the local Hilbert space for each site. Used to check whether the operators need Jordan-Wigner strings.

• op_string (None | str) –

Operator name to be used as operator string between the operators, or None if the Jordan Wigner string should be figured out.

Warning

None figures out for each segment between the operators, whether a Jordan-Wigner string is needed. This is different from a plain 'JW', which just applies a string on each segment!

Returns

Arguments for MultiCouplingTerms.add_multi_coupling_term() such that the added term corresponds to the parameters of this function.

Return type

strength, i, j, op_i, op_j, op_string

plot_coupling_terms(ax, lat, style_map='default', common_style={'linestyle': '--'}, text=None, text_pos=0.4)[source]

“Plot coupling terms into a given lattice.

This function plots the coupling_terms

Parameters
• ax (matplotlib.axes.Axes) – The axes on which we should plot.

• lat (Lattice) – The lattice for plotting the couplings, most probably the M.lat of the corresponding model M, see lat.

• style_map (function | None) – Function which get’s called with arguments i, j, op_i, op_string, op_j, strength for each two-site coupling and should return a keyword-dictionary with the desired plot-style for this coupling. By default (None), the linewidth is given by the absolute value of strength, and the linecolor depends on the phase of strength (using the hsv colormap).

• common_style (dict) – Common style, which overwrites values of the dictionary returned by style_map. A 'label' is only used for the first plotted line.

• text (format_string | None) – If not None, we add text labeling the couplings in the plot. Available keywords are i, j, op_i, op_string, op_j, strength as well as strength_abs, strength_angle, strength_real.

• text_pos (float) – Specify where to put the text on the line between i (0.0) and j (1.0), e.g. 0.5 is exactly in the middle between i and j.

tenpy.models.lattice.Lattice.plot_sites

plot the sites of the lattice.

add_to_graph(graph)[source]

Add terms from coupling_terms to an MPOGraph.

Parameters

graph (MPOGraph) – The graph into which the terms from coupling_terms should be added.

to_nn_bond_Arrays(sites)[source]

Convert the coupling_terms into Arrays on nearest neighbor bonds.

Parameters

sites (list of Site) – Defines the local Hilbert space for each site. Used to translate the operator names into Array.

Returns

H_bond – The coupling_terms rewritten as sum_i H_bond[i] for MPS indices i. H_bond[i] acts on sites (i-1, i), None represents 0. Legs of each H_bond[i] are ['p0', 'p0*', 'p1', 'p1*'].

Return type

list of {Array | None}

remove_zeros(tol_zero=1e-15)[source]

Remove entries close to 0 from coupling_terms.

Parameters

tol_zero (float) – Entries in coupling_terms with strength < tol_zero are considered to be zero and removed.

to_TermList()[source]

Convert onsite_terms into a TermList.

Returns

term_list – Representation of the terms as a list of terms.

Return type

TermList

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 (:classGroup) – HDF5 group which is supposed to represent self.

• subpath (str) – The name of h5gr with a '/' in the end.