CouplingTerms¶

class tenpy.networks.terms.CouplingTerms(L)[source]¶

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

Parameters

Attributes

Lint: Number of sites.
coupling_termsdict of dict: 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.

Methods

`add_coupling_term`(self, strength, i, j, …)	Add a two-site coupling term on given MPS sites.
`add_to_graph`(self, graph)	Add terms from `coupling_terms` to an MPOGraph.
`coupling_term_handle_JW`(self, strength, …)	Helping function to call before `add_multi_coupling_term()`.
`max_range`(self)	Determine the maximal range in `coupling_terms`.
`plot_coupling_terms`(self, ax, lat[, …])	“Plot coupling terms into a given lattice.
`remove_zeros`(self[, tol_zero])	Remove entries close to 0 from `coupling_terms`.
`to_TermList`(self)	Convert `onsite_terms` into a `TermList`.
`to_nn_bond_Arrays`(self, sites)	Convert the `coupling_terms` into Arrays on nearest neighbor bonds.

max_range(self)[source]¶

Determine the maximal range in coupling_terms.

Returns

max_rangeint: The maximum of j - i for the i, j occuring in a term of coupling_terms.

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

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

Parameters

strengthfloat: The strength of the coupling term.
i, jint: 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, op2str: Names of the involved operators.
op_stringstr: The operator to be inserted between i and j.

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

Helping function to call before add_multi_coupling_term().

Parameters

strengthfloat: 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.
siteslist of Site: Defines the local Hilbert space for each site. Used to check whether the operators need Jordan-Wigner strings.
op_stringNone | str: Operator name to be used as operator string between the operators, or None if the Jordan Wigner string should be figured out.

Returns

strength, i, j, op_i, op_j, op_string:: Arguments for MultiCouplingTerms.add_multi_coupling_term() such that the added term corresponds to the parameters of this function.

plot_coupling_terms(self, 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

axmatplotlib.axes.Axes: The axes on which we should plot.
latLattice: The lattice for plotting the couplings, most probably the M.lat of the corresponding model M, see lat.
style_mapfunction | 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_styledict: 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_posfloat: 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.