@@ -576,50 +576,7 @@ def is_finite(syst):

 class InfiniteSystemMixin(metaclass=abc.ABCMeta):

-    """Abstract infinite low-level system.

-

-    An infinite system consists of an infinite series of identical cells.

-    Adjacent cells are connected by identical inter-cell hoppings.

-

-    Attributes

-    ----------

-    cell_size : integer

-        The number of sites in a single cell of the system.

-

-    Notes

-    -----

-    The system graph of an infinite systems contains a single cell, as well as

-    the part of the previous cell which is connected to it.  The first

-    `cell_size` sites form one complete single cell.  The remaining ``N`` sites

-    of the graph (``N`` equals ``graph.num_nodes - cell_size``) belong to the

-    previous cell.  They are included so that hoppings between cells can be

-    represented.  The N sites of the previous cell correspond to the first

-    ``N`` sites of the fully included cell.  When an ``InfiniteSystem`` is used

-    as a lead, ``N`` acts also as the number of interface sites to which it

-    must be connected.

-

-    The drawing shows three cells of an infinite system.  Each cell consists

-    of three sites.  Numbers denote sites which are included into the system

-    graph.  Stars denote sites which are not included.  Hoppings are included

-    in the graph if and only if they occur between two sites which are part of

-    the graph::

-

-            * 2 *

-        ... | | | ...

-            * 0 3

-            |/|/|

-            *-1-4

-

-        <-- order of cells

-    The numbering of sites in the drawing is one of the two valid ones for that

-    infinite system.  The other scheme has the numbers of site 0 and 1

-    exchanged, as well as of site 3 and 4.

-

-    Sites in the fundamental domain cell must belong to a different site array

-    than the sites in the previous cell. In the above example this means that

-    sites '(0, 1, 2)' and '(3, 4)' must belong to different site arrays.

-    """

     @deprecate_args

     def modes(self, energy=0, args=(), *, params=None):

         """Return mode decomposition of the lead

@@ -704,6 +661,46 @@ class InfiniteSystemMixin(metaclass=abc.ABCMeta):

 class InfiniteSystem(System, InfiniteSystemMixin, metaclass=abc.ABCMeta):

+    """Abstract infinite low-level system.

+

+    An infinite system consists of an infinite series of identical cells.

+    Adjacent cells are connected by identical inter-cell hoppings.

+

+    Attributes

+    ----------

+    cell_size : integer

+        The number of sites in a single cell of the system.

+

+    Notes

+    -----

+    The system graph of an infinite systems contains a single cell, as well as

+    the part of the previous cell which is connected to it.  The first

+    `cell_size` sites form one complete single cell.  The remaining ``N`` sites

+    of the graph (``N`` equals ``graph.num_nodes - cell_size``) belong to the

+    previous cell.  They are included so that hoppings between cells can be

+    represented.  The N sites of the previous cell correspond to the first

+    ``N`` sites of the fully included cell.  When an ``InfiniteSystem`` is used

+    as a lead, ``N`` acts also as the number of interface sites to which it

+    must be connected.

+

+    The drawing shows three cells of an infinite system.  Each cell consists

+    of three sites.  Numbers denote sites which are included into the system

+    graph.  Stars denote sites which are not included.  Hoppings are included

+    in the graph if and only if they occur between two sites which are part of

+    the graph::

+

+            * 2 *

+        ... | | | ...

+            * 0 3

+            |/|/|

+            *-1-4

+

+        <-- order of cells

+

+    The numbering of sites in the drawing is one of the two valid ones for that

+    infinite system.  The other scheme has the numbers of site 0 and 1

+    exchanged, as well as of site 3 and 4.

+    """

     @deprecate_args

     def cell_hamiltonian(self, args=(), sparse=False, *, params=None):

@@ -730,6 +727,36 @@ class InfiniteSystem(System, InfiniteSystemMixin, metaclass=abc.ABCMeta):

 class InfiniteVectorizedSystem(VectorizedSystem, InfiniteSystemMixin, metaclass=abc.ABCMeta):

+    """Abstract vectorized infinite low-level system.

+

+    An infinite system consists of an infinite series of identical cells.

+    Adjacent cells are connected by identical inter-cell hoppings.

+

+    Attributes

+    ----------

+    cell_size : integer

+        The number of sites in a single cell of the system.

+

+    Notes

+    -----

+    Unlike `~kwant.system.InfiniteSystem`, vectorized infinite systems do

+    not explicitly store the sites in the previous unit cell; only the

+    sites in the fundamental domain are stored. Nevertheless, the

+    SiteArrays of `~kwant.system.InfiniteVectorizedSystem` are ordered

+    in an analogous way, in order to facilitate the representation of

+    inter-cell hoppings. The ordering is as follows. The *interface sites*

+    of a unit cell are the sites that have hoppings to the *next* unit cell

+    (along the symmetry direction). Interface sites are always in different

+    SiteArrays than non-interface sites, i.e. the sites in a given SiteArray

+    are either all interface sites, or all non-interface sites.

+    The SiteArrays consisting of interface sites always appear *before* the

+    SiteArrays consisting of non-interface sites in ``self.site_arrays``.

+    This is backwards compatible with `kwant.system.InfiniteSystem`.

+

+    For backwards compatibility, `~kwant.system.InfiniteVectorizedSystem`

+    maintains a ``graph``, that includes nodes for the sites

+    in the previous unit cell.

+    """

     cell_hamiltonian = _system.vectorized_cell_hamiltonian

     inter_cell_hopping = _system.vectorized_inter_cell_hopping