Builder fixes

Address issues related to interfacing with kwant, such as qt/kwant-scf#10 and qt/kwant-scf#9.

meanfi/tests/test_kwant.py

@@ -16,28 +16,26 @@ def test_kwant_conversion(seed):
     ndim = np.random.randint(1, 3)
     cutoff = np.random.randint(1, 3)
     sites_in_cell = np.random.randint(1, 4)
-    ndof_per_site = [np.random.randint(1, 5) for site in range(sites_in_cell)]
+    ndof_per_site = [np.random.randint(1, 4) for site in range(sites_in_cell)]
     keyList = generate_tb_keys(cutoff, ndim)
-    n_cells = np.random.randint(4)
+
+    vecs = np.random.rand(ndim, ndim)
 
     # set a dummy lattice to read sites from
     lattice = kwant.lattice.general(
-        np.random.rand(ndim, ndim),
-        basis=np.random.rand(sites_in_cell, ndim),
+        vecs,
+        basis=np.random.rand(sites_in_cell, ndim) @ vecs,
         norbs=ndof_per_site,
     )
 
-    dummy_tb = kwant.Builder(
-        kwant.TranslationalSymmetry(*n_cells * lattice.prim_vecs)
-    )
-    for site in range(sites_in_cell):
-        for sublattice in lattice.sublattices:
-            dummy_tb[sublattice(site, *[0 for _ in range(ndim - 1)])] = (
-                np.eye(sum(ndof_per_site)) * 2
-            )
+    dummy_tb = kwant.Builder(kwant.TranslationalSymmetry(*lattice.prim_vecs))
+    for i, sublattice in enumerate(lattice.sublattices):
+        dummy_tb[lattice.shape(lambda pos: True, tuple(ndim * [0]))] = np.eye(
+            ndof_per_site[i]
+        )
 
     # generate random and generate builder from it
-    random_tb = guess_tb(keyList, sum(ndof_per_site) * sites_in_cell * n_cells)
+    random_tb = guess_tb(keyList, sum(ndof_per_site))
     random_builder = tb_to_builder(
         random_tb, list(dummy_tb.sites()), dummy_tb.symmetry.periods
     )