Fix 2D RBC

Author: brownbaerchen

pySDC/implementations/problem_classes/RayleighBenard.py

@@ -213,12 +213,8 @@ def eval_f(self, u, *args, **kwargs):
 
         # start by computing derivatives
         if not hasattr(self, '_Dx_expanded') or not hasattr(self, '_Dz_expanded'):
-            self._Dx_expanded = self._setup_operator(
-                {'u': {'u': Dx}, 'v': {'v': Dx}, 'T': {'T': Dx}, 'p': {}}, diag=True
-            )
-            self._Dz_expanded = self._setup_operator(
-                {'u': {'u': Dz}, 'v': {'v': Dz}, 'T': {'T': Dz}, 'p': {}}, diag=True
-            )
+            self._Dx_expanded = self._setup_operator({'u': {'u': Dx}, 'v': {'v': Dx}, 'T': {'T': Dx}, 'p': {}})
+            self._Dz_expanded = self._setup_operator({'u': {'u': Dz}, 'v': {'v': Dz}, 'T': {'T': Dz}, 'p': {}})
         Dx_u_hat = (self._Dx_expanded @ u_hat.flatten()).reshape(u_hat.shape)
         Dz_u_hat = (self._Dz_expanded @ u_hat.flatten()).reshape(u_hat.shape)