Previously we used the ExtensionUnavailable proxy that would
raise an exception when accessed. Now because kwant.continuum
is loaded lazily we can just raise an exception. We choose to
re-raise ImportError with a better error message.

'matplotlib', 'Figure', '_colormaps', 'mpl_available', 'mplot3d',
'has3d', 'LineCollection', 'PathCollection', 'Line3DCollection',
and 'Path3DCollection'.

We will need to issue deprecation warnings when using this with
'kwant.continuum', so we have to roll our own so we can hook into
the attribute access. When we no longer need this feature we
can replace this with a simpler implementation using
'importlib.util.LazyLoader'.

Without this the test for whether importing the plotter chooses
the matplotlib backend fails when matplotlib is not installed.

This was forgotten in !199.

Thanks to Tibor Sekera for suggesting this feature.

remove use of 'vector_factory' when calculating spectral bounds

Closes #184

See merge request kwant/kwant!201

Pablo Piskunow authored 7 years ago and Joseph Weston committed 7 years ago

Instead, use a random phase vector. Now 'vector_factory' is used
exclusively to generate the vectors used in the KPM calculation
itself.

Matplotlib backends like PDF cannot display arbitrarily thin lines.
That's why kwant.plotter.streamplot simulates thinner lines by blending
them into the background.

Previously if no lines were blended, i.e. all had the same color value
1, the background color would be used for drawing them instead of the
line color.

Bas Nijholt authored 7 years ago and Anton Akhmerov committed 7 years ago

Closes #182

Closes #182

version 1.3.2

This commit fixes the bug in phs_symmetrization when it fails to produce ph eigenstates
with PH^2 = +1 when one of the wave functions is mapped exactly onto another one by PH,
as in this case the PH symmetrized wf's from the two are identical. This is the case
with wfs = np.eye(2) and  particle_hole = sigma[1], the second vector returned is an
eigenstate with eigenvalue -1 not +1. In general this can be even worse, if there are
multiple such vector pairs some vectors may not be ph eigenstates at all.

The new code uses an improved version of the matrix square root method from
Applied Mathematics and Computation 234 (2014) 380-384.

Tests are modified to clear up the random unitary generation process (using kwant.rmt).
Tests are now guaranteed to feed orthonormal set of vectors to phs_symmetrization().
Add extra tests for the fully off-diagonal case where the old method fails.

Previously, in order to not to fix the matplotlib backend, we required
users to import matplotlib.pyplot before calling any Kwant plotting
functions.  This did not have the desired effect, since we did import
`matplotlib.backends` and that also fixes the backend.

Now, both backends and pyplot are imported at the last possible moment
and a warning is emitted if this fixes the backend.

The problem was introduced in commit 7c802539.

Closes #47.

Previously it was never made explicit that the current
returned from an operator is ordered like the system graph, or
that the density is ordered as the sites of the system.

Closes #172.

Backport deprecation warning fixes from 'master' to 'stable'
(these changes should have been applied to 'stable' directly).

The lead does not have connected unit cells and serves no purpose.
We also remove the check for the number of 'collections' in the
resulting plots, as now both 'syst_2d' and 'syst_3d' produce
systems with 2 leads.