CHANGELOG.rst

CHANGELOG

All notable changes to the project will be documented in this file. The project adheres semantic versioning

[Unreleased]

Backwards incompatible changes

• The argument order of :class:`tenpy.models.lattice.Lattice` could be a tuple (priority, snake_winding) before. This is no longer valid and needs to be replaced by ("standard", snake_winding, priority).
• Moved the boundary conditions bc_coupling from the :class:`tenpy.models.model.CouplingModel` into the :class:`tenpy.models.lattice.Lattice` (as bc). Using the parameter bc_coupling will raise a FutureWarning, one should set the boundary conditions directly in the lattice.

Added

• :meth:`tenpy.networks.mps.MPS.canonical_form_infinite`.
• :meth:`tenpy.linalg.np_conserved.Array.extend` and :meth:`tenpy.linalg.charges.LegCharge.extend`, allowing to extend an Array with zeros.
• DMRG parameter 'orthogonal_to' allows to calculate excited states for finite systems.
• possibility to change the number of charges after creating LegCharges/Arrays
• more general way to specify the order of sites in a :class:`tenpy.models.lattice.Lattice`.
• new :class:`tenpy.models.lattice.Honeycomb` and :class:`tenpy.models.lattice.Kagome` lattice
• a way to specify nearest neighbor couplings in a :class:`~tenpy.models.lattice.Lattice`, along with methods to count the number of nearest neighbors for sites in the bulk, and a way to plot them (:meth:`~tenpy.models.lattice.plot_coupling` and friends)
• :meth:`tenpy.networks.mpo.MPO.from_grids` to generate the MPO from a grid.
• :class:`tenpy.models.model.MultiCouplingModel` for couplings involving more than 2 sites.
• request #8: Allow shift in boundary conditions of :class:`~tenpy.models.model.CouplingModel`.

Changed

• moved toycodes from the folder examples/ to a new folder toycodes/ to separate them clearly.
• Restructured lanczos into a class, added time evolution calculating exp(A*dt)|psi0>
• Warning for poorly conditioned Lanczos; to overcome this enable the new parameter "reortho"
• By default, make deep copies of npc Arrays.
• Restructured :mod:`tenpy.algorithms.dmrg`:
  • :func:`~tenpy.algorithms.dmrg.run` is now just a wrapper around the new :meth:`~tenpy.algorithms.dmrg.Engine.run`, run(psi, model, pars) is roughly equivalent to eng = EngineCombine(psi, model, pars); eng.run().
  • Added :meth:`~tenpy.algorithms.dmrg.Engine.init_env` and :meth:`~tenpy.algorithms.dmrg.Engine.reset_stats` to allow a simple restart of DMRG with slightly different parameters.
  • call MPS.canonical_form() for infinite systems if the final state is not in canonical form.
• Changed default values for some parameters:
  • increase Lanczos_params['N_cache'] = N_max (i.e. keep all states)
  • set DMRG_params['P_tol_to_trunc'] = 0.05 and provide reasonable ..._min and ..._max values.
  • increased (default) DMRG accuracy by setting DMRG_params['max_E_err'] = 1.e-5 and DMRG_params['max_S_err'] = 1.e-3.
• Don't print the energy during real-time TEBD evolution - it's preserved up to truncation errors.
• Renamed the SquareLattice class to :class:`tenpy.models.lattice.Square` for better consistency.
• auto-determine whether Jordan-Wigner strings are necessary in :meth:`~tenpy.models.model.CouplingModel.add_coupling`.

Fixed

• avoid error in MPS.apply_local_op()
• Don't carry around total charge when using DMRG with a mixer
• Corrected couplings of the FermionicHubbardChain
• issue #2: memory leak in cython parts when using intelpython/anaconda
• issue #4: incompatible data types.
• issue #6: the CouplingModel generated wrong Couplings in some cases
• more reasonable traceback in case of wrong labels

Removed

• Attribute chinfo of :class:`~tenpy.models.lattice.Lattice`.

[0.3.0] - 2018-02-19

This is the first version published on github.

Added

• Cython modules for np_conserved and charges, which can optionally compiled for speed-ups
• tools.optimization for dynamical optimization
• Various models.
• More predefined lattice sites.
• Example toy-codes.
• Network contractor for general networks

Changed

• Switch to python3

Removed

• Python 2 support.

[0.2.0] - 2017-02-24

• Compatible with python2 and python3 (using the 2to3 tool).
• Development version.
• Includes TEBD and DMRG.

Changes compared to previous TeNPy

This library is based on a previous (closed source) version developed mainly by Frank Pollmann, Michael P. Zaletel and Roger S. K. Mong. While allmost all files are completely rewritten and not backwards compatible, the overall structure is similar. In the following, we list only the most important changes.

Global Changes

• syntax style based on PEP8. Use $>yapf -r -i ./ to ensure consitent formatting over the whole project. Special comments # yapf: disable and # yapf: enable can be used for manual formatting of some regions in code.

• Following PEP8, we distinguish between 'private' functions, indicated by names starting with an underscore and to be used only within the library, and the public API. The puplic API should be backwards-compatible with different releases, while private functions might change at any time.

• all modules are in the folder tenpy to avoid name conflicts with other libraries.

• withing the library, relative imports are used, e.g., from ..tools.math import (toiterable, tonparray) Exception: the files in tests/ and examples/ run as __main__ and can't use relative imports

  Files outside of the library (and in tests/, examples/) should use absolute imports, e.g. import tenpy.algorithms.tebd

• renamed tenpy/mps/ to tenpy/networks, since it containes various tensor networks.

• added :class:`~tenpy.networks.site.Site` describing the local physical sites by providing the physical LegCharge and onsite operators.

np_conserved

• pure python, no need to compile!
• in module :mod:`tenpy.linalg` instead of algorithms/linalg.
• moved functionality for charges to :mod:`~tenpy.linalg.charges`
• Introduced the classes :class:`~tenpy.linalg.charges.ChargeInfo` (basically the old q_number, and mod_q) and :class:`~tenpy.linalg.charges.LegCharge` (the old qind, qconj).
• Introduced the class :class:`~tenpy.linalg.charges.LegPipe` to replace the old leg_pipe. It is derived from LegCharge and used as a leg in the array class. Thus any inherited array (after tensordot etc still has all the necessary information to split the legs. (The legs are shared between different arrays, so it's saved only once in memory)
• Enhanced indexing of the array class to support slices and 1D index arrays along certain axes
• more functions, e.g. :func:`~tenpy.linalg.np_conserved.grid_outer`

TEBD

• Introduced TruncationError for easy handling of total truncation error.
• some truncation parameters are renamed and may have a different meaning, e.g. svd_max -> svd_min has no 'log' in the definition.

DMRG

• separate Lanczos module in tenpy/linalg/. Strangely, the old version orthoganalized against the complex conjugates of orthogonal_to (contrary to it's doc string!) (and thus calculated 'theta_o' as bra, not ket).
• cleaned up, provide prototypes for DMRG engine and mixer.

Tools

• added :mod:`tenpy.tools.misc`, which contains 'random stuff' from old tools.math like to_iterable and to_array (renamed to follow PEP8, documented)
• moved stuff for fitting to :mod:`tenpy.tools.fit`
• enhanced :func:`tenpy.tools.string.vert_join` for nice formatting
• moved (parts of) old cluster/omp.py to :mod:`tenpy.tools.process`
• added :mod:`tenpy.tools.params` for a simplified handling of parameter/arguments for models and/or algorithms. Similar as the old models.model.set_var, but use it also for algorithms. Also, it may modify the given dictionary.