Hi everyone,
> This is very strange; when I download the notebook and run it I indeed
> see the error that you reported, however when I try to run the
> following minimal example it succeeds:
>
>
>> import numpy as np
>> import matplotlib.pyplot
>> import kwant
>>
>> graphene = kwant.lattice.general([[1, 0], [1/2, np.sqrt(3)/2]], #
>> lattice vectors
>> [[0, 0], [0, 1/np.sqrt(3)]]) #
>> Coordinates of the sites
>>
>> zigzag_ribbon = kwant.Builder(kwant.TranslationalSymmetry([1, 0]))
>> zigzag_ribbon[graphene.shape((lambda pos: abs(pos[1]) < 9), (0, 0))] = 0
>> zigzag_ribbon[graphene.neighbors(1)] = 1
>>
>> print(kwant.__version__)
>> kwant.plot(zigzag_ribbon);
>
> I'll investigate a bit more and report my results.
>
Found it! In Kwant 1.4.0a1 we tweaked Kwant's plotting so that sites
from different families (sublattices) would use the colors from
Matplotlib's color cycle by default. In the March Meeting tutorial
notebooks there is a line:
> %run matplotlib_setup.ipy
that loads some custom matplotlib setup to make the plots look a bit
better in the notebooks. Looking into 'matplotlib_setup.ipy' we see the
following suspicious line:
> mpl.rc('axes', prop_cycle=mpl.cycler('color', ['black']))
which was included to stop all the bandstructure plots being
multicolored (because it's distracting), however because there are fewer
colors than there are site families (2 site families in graphene) the
color cycling in Kwant's plotter broke.
This is a bug in Kwant, and I've opened an issue [1] on our bugtracker.
I'll fix this today and it'll go into the v1.4.0 release (that we will
make sometime between now and christmas).
In the short term you can fix this in a couple of ways:
+ either downgrade to Kwant 1.3.3
+ or change the offending line in 'matplotlib_setup.ipy' to:
mpl.rc('axes', prop_cycle=mpl.cycler('color', ['black', 'black']))
+ or wait until I push a change to the tutorial notebooks later today
and then re-download them
Thanks for the report, and happy kwanting!
Joe
[1]: https://gitlab.kwant-project.org/kwant/kwant/issues/257
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