Fix extract_states preservation hermiticity.

doc/changes/2214.bugfix

@@ -0,0 +1,2 @@
+Fixed issue where `extrac_states` did not preserve hermiticity.
+Fixed issue where `rand_herm` did not set the private attribute _isherm to True.

qutip/qobj.py

@@ -1843,7 +1843,7 @@ def extract_states(self, states_inds, normalize=False):
 
         """
         if self.isoper:
-            q = Qobj(self.data[states_inds, :][:, states_inds])
+            q = Qobj(self.data[states_inds, :][:, states_inds], isherm=self._isherm or None)
         elif self.isket:
             q = Qobj(self.data[states_inds, :])
         elif self.isbra:

qutip/random_objects.py

@@ -137,7 +137,7 @@ def rand_herm(N, density=0.75, dims=None, pos_def=False, seed=None):
             M = _rand_herm_dense(N, density, pos_def)
     else:
         raise TypeError('Input N must be an integer or array_like.')
-    return Qobj(M, dims=dims)
+    return Qobj(M, dims=dims, isherm=True)
 
 
 def _rand_herm_sparse(N, density, pos_def):

qutip/tests/test_qobj.py

@@ -1012,6 +1012,14 @@ def test_overlap():
         assert np.allclose(Ad.overlap(Bd), ans)
         assert np.allclose(A.overlap(Bd), np.conj(ans))
 
+def test_extract_states_hermiticity():
+    """Test that hermiticity is preserved after extract_states."""
+
+    H_t = rand_herm(10, seed=0)
+    H_t_reduced = H_t.extract_states(range(3))
+
+    assert H_t_reduced._isherm == True
+
 
 def test_unit():
     """