hello everyone. I am trying to plot r=the band structure of 3 d structure .but getting an error.Please tell me how to deal with 3 d structures?my code is this: import kwant from matplotlib import pyplot import math import numpy as np import cmath lat = kwant.lattice.general([(0, 0.5, 0.5), (0.5, 0, 0.5), (0.5, 0.5, 0)], [(0, 0, 0), (0.25, 0.25, 0.25)]) a, b = lat.sublattices def make_cuboid(a=2, b=2, c=2): def cuboid_shape(pos): x, y, z = pos return 0 <= x < a and 0 <= y < b and 0 <= z < c sym = kwant.TranslationalSymmetry(lat.vec((-1,-1,-1))) sys = kwant.Builder(sym) sys[lat.shape(cuboid_shape, (0, 0, 0))] = None sys[lat.neighbors()] = None return sys sys = make_cuboid() sys = sys.finalized() kwant.plotter.bands(sys, momenta= np.linspace(-5,5,10000),show=False) pyplot.xlabel("momentum [(lattice constant)^-1]") pyplot.ylabel("energy [t]") pyplot.show() The error is :TypeError: a float is required