Prevent usage of adaptive steppers with stochastic PDEs (#633)

Author: david-zwicker

pde/solvers/base.py

@@ -673,6 +673,10 @@ def make_stepper(
             # create stepper with fixed steps
             return super().make_stepper(state, dt)
 
+        if getattr(self.pde, "is_sde", False):
+            # adaptive steppers cannot deal with stochastic PDEs
+            raise RuntimeError("Cannot use adaptive stepper with stochastic equation")
+
         # Support `None` as a default value, so the controller can signal that
         # the solver should use a default time step.
         if dt is None:

pde/solvers/explicit.py

@@ -386,9 +386,6 @@ def _make_adaptive_stepper(
                 An example for the state from which the grid and other information can
                 be extracted
         """
-        if self.pde.is_sde:
-            raise RuntimeError("Cannot use adaptive stepper with stochastic equation")
-
         self.info["scheme"] = self.scheme
         if self.scheme == "euler":
             return self._make_adaptive_euler_stepper(state)