add a single comprehensive test of most of kwant (QHE plateaus)

kwant/tests/test_comprehensive.py

+import math
+from cmath import exp
+import kwant
+from kwant.contrib.digest import gauss
+
+
+def hopping(sitei, sitej, phi, salt):
+    xi, yi = sitei.pos
+    xj, yj = sitej.pos
+    return -exp(-0.5j * phi * (xi - xj) * (yi + yj))
+
+
+def onsite(site, phi, salt):
+    return 0.3 * gauss(repr(site), salt) + 4
+
+
+def test_qhe(W=16, L=8):
+    def central_region(pos):
+        x, y = pos
+        return -L < x < L and \
+            abs(y) < W - 5.5 * math.exp(-x**2 / 5**2)
+
+    lat = kwant.lattice.square()
+    sys = kwant.Builder()
+
+    sys[lat.shape(central_region, (0, 0))] = onsite
+    sys[lat.neighbors()] = hopping
+
+    lead = kwant.Builder(kwant.TranslationalSymmetry((-1, 0)))
+    lead[(lat(0, y) for y in range(-W + 1, W))] = 4
+    lead[lat.neighbors()] = hopping
+
+    sys.attach_lead(lead)
+    sys.attach_lead(lead.reversed())
+    sys = sys.finalized()
+
+    #### The following chunk of code can be uncommented to visualize the
+    #### conductance plateaus.
+    # from matplotlib import pyplot
+    # import numpy
+    # reciprocal_phis = numpy.linspace(0.1, 7, 200)
+    # conductances = []
+    # for phi in 1 / reciprocal_phis:
+    #     smatrix = kwant.solve(sys, 1.0, args=[phi, ""])
+    #     conductances.append(smatrix.transmission(1, 0))
+    # pyplot.plot(reciprocal_phis, conductances)
+    # pyplot.show()
+
+    for r_phis, T_nominal, max_err in [((1.3, 2.1), 1, 1e-7),
+                                       ((3.2, 3.7), 2, 1e-3),
+                                       ((5.2, 5.5), 3, 1e-1)]:
+        for r_phi in r_phis:
+            args = (1.0 / r_phi, "")
+            T_actual = kwant.solve(sys, 1.0, args=args).transmission(1, 0)
+            assert abs(T_nominal - T_actual) < max_err