Cyten - a combination of Cytnx and TeNPy

The name Cyten is pronounced like sci-ten, and refers to scientific tensor networks implmented in C++ with a focus on the provided Python bindings, and the python-style library in modern C++.

About: combining forces of the TeNPy and Cytnx team

This repo originates from a collaboration between the Cytnx and TeNPy developers. Cytnx is a C++ library for Tensors with Abelian symmetries with pybind11 bindings to Python. The goal is to use that as a basis to translate the refactoring and implementation of non-Abelian symmetries from the v2_alpha branch in the tenpy repository (currenlty in pure Python) into C++, thereby extending the capabilities of the cytnx library, and providing a backend for TeNpy which will then focus on the higher-levels (defining MPS and algorithms like DMRG etc). At the same time, the code from cytnx to be included will be refactored and cleaned a bit.

Setup

Once released, we will provide pre-compiled packages on conda/pip. Until then, you need to build the package yourself on your local machine, as detailed in docs/INSTALL.rst.

Testing

The python interface is tested with pytest run from the tests/ folder in the repo. To test the C++ code, run gtest (from GoogleTest).

Documentation

Will eventually be online, but so far you also need to build it locally. See README.md in the docs/ folder on how - essentially just install cyten, run doxygen and then make html in the docs/ folder.

Code style and linting

Please follow these guidelines when contributing code

• Use a code style based on :pep:8. The git repo includes a config file .flake8 for the python package flake8 <https://flake8.pycqa.org/en/latest/>_. flake8 is a tool that lints python code, i.e. it checks a number of rules for code formatting and reports any violations. Install it using either pip or conda. Run e.g. flake8 . in the repository root. Feel free to use the git hooks, see docs/contributing/code_style.rst. It is recommended to also install the flake8-docstring <https://github.com/pycqa/flake8-docstrings> extension.

• Every function/class/module should be documented by its doc-string, see :pep:257. Exception: If you override a method of a parent class, only add a docstring if it adds value.

  Additional documentation for the user guide is in the folder doc/.

  The documentation uses reStructuredText. If you are new to reStructuredText, read this introduction <http://www.sphinx-doc.org/en/stable/rest.html>. We use the numpy style for doc-strings (with the napoleon <https://www.sphinx-doc.org/en/master/usage/extensions/napoleon.html> extension to sphinx). You can read about them in these Instructions for the doc strings <https://numpydoc.readthedocs.io/en/latest/format.html>. In addition, you can take a look at the following example file <https://github.com/numpy/numpydoc/blob/main/doc/example.py>. Helpful hints on top of that::

    r"""<- this r makes me a raw string, thus '\' has no special meaning.
    Otherwise you would need to escape backslashes, e.g. in math formulas.
  
    You can include cross references to classes, methods, functions, modules like
    :class:`~tenpy.linalg.np_conserved.Array`, :meth:`~tenpy.linalg.np_conserved.Array.to_ndarray`,
    :func:`tenpy.tools.math.toiterable`, :mod:`tenpy.linalg.np_conserved`.
    The ~ in the beginning makes only the last part of the name appear in the generated documentation.
    Documents of the userguide can be referenced with :doc:`/intro_npc` even from inside the doc-strings.
    You can also cross-link to other documentations, e.g. :class:`numpy.ndarray`, :func`scipy.linalg.svd` and :mod: will work.
  
    Moreover, you can link to github issues, arXiv papers, dois, and topics in the community forum with
    e.g. :issue:`5`, :arxiv:`1805.00055`, :doi:`10.1000/1` and :forum:`3`.
  
    Citations from the literature list can be cited as :cite:`white1992` using the bibtex key.
  
    Write inline formulas as :math:`H |\Psi\rangle = E |\Psi\rangle` or displayed equations as
    .. math ::
  
       e^{i\pi} + 1 = 0
  
    In doc-strings, math can only be used in the Notes section.
    To refer to variables within math, use `\mathtt{varname}`.
  
    .. todo ::
  
       This block can describe things which need to be done and is automatically included in a section of :doc:`todo`.
    """
  

• Use relative imports within the package. Example::

  from .symmetries import no_symmetry
  

• If you write new functions, please also include suitable tests!

• During development, you might introduce # TODO comments. Please use exactly this format, to make searching for them easier, and include your initials or name. Try to remove/resolve them as soon as possible. If you're not 100% sure that you will remove it soon, please add a doc-string with a .. todo :: block, such that we can keep track of it.

  Unfinished functions should raise NotImplementedError().

• We may start keeping a changelog in the future, so far we do not.