add checks for non-matching boundary conditions

tkwant/onebody/onebody.py

@@ -270,6 +270,9 @@ class WaveFunction:
             time_is_valid = extended_system.time_is_valid
         else:
             # true finite systems (no leads) so no need for boundary conditions
+            if boundaries is not None:
+                raise ValueError('No boundary conditions must be provided '
+                                 'for a system without leads.')
             H0 = syst.hamiltonian_submatrix(params=tparams, sparse=True)
             solution_is_valid = None
             time_is_valid = None

tkwant/onebody/tests/test_solvers.py

@@ -798,6 +798,14 @@ def test_WaveFunction_open_system__init__raises(psi_init, syst, energy, params):
 @closed_sytem()
 def test_WaveFunction_closed_system__init__raises(psi_init, syst, energy, params):
 
+    # provide boundaries to a closed system
+    boundaries, tmax = make_boundaries(nb_leads=len(syst.leads), tmax=6)
+    with pytest.raises(ValueError) as exc:
+        WaveFunction.from_kwant(psi_init=psi_init, syst=syst, boundaries=boundaries,
+                                energy=energy, params=params)
+    msg = 'No boundary conditions must be provided for a system without leads.'
+    assert msg in str(exc.value)
+
     params_with_time = params.copy()
     params_with_time['time'] = 0
     with pytest.raises(KeyError) as exc:

tkwant/system.py

@@ -305,6 +305,12 @@ def hamiltonian_with_boundaries(syst, boundaries, params):
         The Hamiltonian of the central system, evaluated at t=0,
         with boundary conditions attached, and accompanying metadata.
     """
+
+    if not len(syst.leads) == len(boundaries):
+        raise ValueError('Number of leads= {} does not match '
+                         'the number of boundaries provided= {}'
+                         .format(len(syst.leads), len(boundaries)))
+
     # generate time-independent Hamiltonian and boundary condition
     # matrices and glue them together
     boundaries = [bc(lead, params) for lead, bc in zip(syst.leads, boundaries)]

tkwant/tests/test_system.py

@@ -221,6 +221,26 @@ def test_hamiltonian(lead_maker):
     assert not Hext.time_is_valid(tmax + eps)
 
 
+@pytest.mark.parametrize('lead_maker', [make_simple_lead])
+def test_hamiltonian_with_boundaries_exceptions(lead_maker):
+
+    # construct
+    syst = make_system_with_leads(kwant.lattice.square(norbs=1), lead_maker)
+    fsyst = syst.finalized()
+
+    # too less boundary conditions
+    boundaries = [leads.SimpleBoundary(10)]
+    with pytest.raises(ValueError) as exc:
+        system.hamiltonian_with_boundaries(fsyst, boundaries, params={})
+    assert 'Number of leads= 2 does not match the number of boundaries provided= 1' in str(exc.value)
+
+    # too many boundary conditions
+    boundaries = [leads.SimpleBoundary(10)] * 3
+    with pytest.raises(ValueError) as exc:
+        system.hamiltonian_with_boundaries(fsyst, boundaries, params={})
+    assert 'Number of leads= 2 does not match the number of boundaries provided= 3' in str(exc.value)
+
+
 def test_is_time_dependent_function():
     def time_dependent(zeit):
         pass