Closes #214.

Closes #295.

The function which finds the symmetries of kwant builders does not find all real space symmetries if the unit cell contains more than one sites, because the conversion from builder to qsymm model does not use a basis which preserves information on the real space position of sites. The tests do not catch this, because they only have one site per unit cell. This fixes the basis choice, and adds a test.

Since this does not seem to justify a new bugfix release of Kwant 1.3,
I apply this commit to the 1.4 stable branch.

When System.parameters was introduced, we thought it would be a good idea to
also use this new attribute.  The plan was to check in hamiltonian_submatrix()
whether any unneeded parameters are provided by the user.  This turned out to
be impossible, so the only check that remained was whether all the necessary
parameters are indeed provided.  However, this check is not necessary, because
the 'hamiltonian' method is in any way obliged to signal an error when it does
not obtain the necessary parameters.

closes #283

This is a workaround for
kwant/kwant#280
and should be reviewed once that issue has been dealt with.

In order not to complicate the licensing situation of Kwant proper,
the new logo will be maintained in a separate repository.

This is a partial application of the changeset proposed in
kwant/kwant!274,
which removes the need for a 'conftest.py', instead using
'pytest.importorskip'.

We apply this change only to 'qsymm', as applying this change elsewhere
requires rethinking where tests are put in the package structure of
Kwant. This minimal change allows us to build packages for Conda and
Debian, which is necessary for releasing Kwant 1.4.

This allows subclassing of operators by third party libraries
(e.g. tkwant).

This shouldn't be a problem, but sphinx complains.

'temp' is too short a parameter name, especially for an API,
and could be confused with 'temporary'.

Deprecate 'args' parameter in favor of 'params'

Closes #272

See merge request kwant/kwant!280

Some tests are explicitly checking the use of 'args'
against the use of 'params', so these we leave in and
instead suppress the warnings.

Additionally update all associated docstrings to say that 'args'
is deprecated in favor of 'params'.

Also implement a specialization of this decorator for the 'args'
parameter, so as to avoid boilerplate (i.e. redefining the help
string everywhere the decorator is used).

The deprecation decorator can also be called directly with no
parameters to raise the warning. This is necessary because
methods of Cython cdef classes do not seem to play well with
this decorator (even after applying @cython.bind(True)), so
we need to call it directly from the body of the method.

Christoph Groth authored 6 years ago and Joseph Weston committed 6 years ago

This allows third party modules to subclass Kwant's cdef classes.
https://cython.readthedocs.io/en/latest/src/userguide/sharing_declarations.html#search-paths-for-definition-files

This means we don't need to create a dummy class that implements
__get__ just so we can use hamiltonian_submatrix as a method.