Added option to skip dt change if insignificant (#482)

pySDC/implementations/convergence_controller_classes/adaptivity.py

@@ -52,7 +52,7 @@ def dependencies(self, controller, description, **kwargs):
         Returns:
             None
         """
-        step_limiter_keys = ['dt_min', 'dt_max', 'dt_slope_min', 'dt_slope_max']
+        step_limiter_keys = ['dt_min', 'dt_max', 'dt_slope_min', 'dt_slope_max', 'dt_rel_min_slope']
         available_keys = [me for me in step_limiter_keys if me in self.params.__dict__.keys()]
 
         if len(available_keys) > 0:

pySDC/implementations/convergence_controller_classes/step_size_limiter.py

@@ -39,7 +39,7 @@ def dependencies(self, controller, description, **kwargs):
         Returns:
             None
         """
-        slope_limiter_keys = ['dt_slope_min', 'dt_slope_max']
+        slope_limiter_keys = ['dt_slope_min', 'dt_slope_max', 'dt_rel_min_slope']
         available_keys = [me for me in slope_limiter_keys if me in self.params.__dict__.keys()]
 
         if len(available_keys) > 0:
@@ -90,7 +90,9 @@ class StepSizeSlopeLimiter(ConvergenceController):
     """
     Class to set limits to adaptive step size computation during run time
 
-    Please supply dt_min or dt_max in the params to limit in either direction
+    Please supply `dt_slope_min` or `dt_slope_max` in the params to limit in either direction.
+    You can also supply `dt_rel_min_slope` in order to keep the old step size in case the relative change is smaller
+    than this minimum.
     """
 
     def setup(self, controller, params, description, **kwargs):
@@ -109,6 +111,7 @@ def setup(self, controller, params, description, **kwargs):
             "control_order": 91,
             "dt_slope_min": 0,
             "dt_slope_max": np.inf,
+            "dt_rel_min_slope": 0,
         }
         return {**defaults, **super().setup(controller, params, description, **kwargs)}
 
@@ -143,5 +146,11 @@ def get_new_step_size(self, controller, S, **kwargs):
                         S,
                     )
                     L.status.dt_new = dt_new
+                elif abs(L.status.dt_new / L.params.dt - 1) < self.params.dt_rel_min_slope:
+                    L.status.dt_new = L.params.dt
+                    self.log(
+                        f"Step size did not change sufficiently to warrant step size change, keeping {L.status.dt_new:.2e}",
+                        S,
+                    )
 
         return None

pySDC/tests/test_convergence_controllers/test_adaptivity.py

@@ -13,7 +13,6 @@ def get_controller(dt, num_nodes, useMPI, adaptivity, adaptivity_params, **kwarg
         adaptivity_params (dict): Parameters for convergence controller
 
     Returns:
-       (dict): Stats object generated during the run
        (pySDC.Controller.controller): Controller used in the run
     """
     from pySDC.implementations.problem_classes.polynomial_test_problem import polynomial_testequation

pySDC/tests/test_convergence_controllers/test_step_size_limiter.py

@@ -0,0 +1,112 @@
+import pytest
+
+
+def get_controller(step_size_limier_params):
+    """
+    Runs a single advection problem with certain parameters
+
+    Args:
+        step_size_limier_params (dict): Parameters for convergence controller
+
+    Returns:
+       (pySDC.Controller.controller): Controller used in the run
+    """
+    from pySDC.implementations.problem_classes.polynomial_test_problem import polynomial_testequation
+    from pySDC.implementations.controller_classes.controller_nonMPI import controller_nonMPI
+    from pySDC.implementations.sweeper_classes.generic_implicit import generic_implicit
+    from pySDC.implementations.convergence_controller_classes.step_size_limiter import StepSizeLimiter
+
+    level_params = {}
+    level_params['dt'] = 1.0
+    level_params['restol'] = 1.0
+
+    sweeper_params = {}
+    sweeper_params['quad_type'] = 'GAUSS'
+    sweeper_params['num_nodes'] = 1
+    sweeper_params['do_coll_update'] = True
+
+    problem_params = {'degree': 10}
+
+    step_params = {}
+    step_params['maxiter'] = 0
+
+    controller_params = {}
+    controller_params['logger_level'] = 30
+
+    description = {}
+    description['problem_class'] = polynomial_testequation
+    description['problem_params'] = problem_params
+    description['sweeper_class'] = generic_implicit
+    description['sweeper_params'] = sweeper_params
+    description['level_params'] = level_params
+    description['step_params'] = step_params
+    description['convergence_controllers'] = {StepSizeLimiter: step_size_limier_params}
+
+    controller = controller_nonMPI(num_procs=1, controller_params=controller_params, description=description)
+
+    controller.add_convergence_controller(StepSizeLimiter, description, step_size_limier_params)
+
+    return controller
+
+
+@pytest.mark.base
+def test_step_size_slope_limiter():
+    from pySDC.implementations.convergence_controller_classes.step_size_limiter import StepSizeSlopeLimiter
+
+    params = {'dt_slope_max': 2, 'dt_slope_min': 1e-3, 'dt_rel_min_slope': 1e-1}
+    controller = get_controller(params)
+
+    limiter = controller.convergence_controllers[
+        [type(me) for me in controller.convergence_controllers].index(StepSizeSlopeLimiter)
+    ]
+
+    S = controller.MS[0]
+    S.status.slot = 0
+    L = S.levels[0]
+    L.status.time = 0
+
+    L.params.dt = 1
+    L.status.dt_new = 3
+    limiter.get_new_step_size(controller, S)
+    assert L.status.dt_new == 2
+
+    L.params.dt = 1
+    L.status.dt_new = 0
+    limiter.get_new_step_size(controller, S)
+    assert L.status.dt_new == 1e-3
+
+    L.params.dt = 1
+    L.status.dt_new = 1 + 1e-3
+    limiter.get_new_step_size(controller, S)
+    assert L.status.dt_new == 1
+
+
+@pytest.mark.base
+def test_step_size_limiter():
+    from pySDC.implementations.convergence_controller_classes.step_size_limiter import StepSizeLimiter
+
+    params = {'dt_max': 2, 'dt_min': 0.5}
+    controller = get_controller(params)
+
+    limiter = controller.convergence_controllers[
+        [type(me) for me in controller.convergence_controllers].index(StepSizeLimiter)
+    ]
+
+    S = controller.MS[0]
+    S.status.slot = 0
+    L = S.levels[0]
+    L.status.time = 0
+
+    L.params.dt = 1
+    L.status.dt_new = 3
+    limiter.get_new_step_size(controller, S)
+    assert L.status.dt_new == 2
+
+    L.params.dt = 1
+    L.status.dt_new = 0
+    limiter.get_new_step_size(controller, S)
+    assert L.status.dt_new == 0.5
+
+
+if __name__ == '__main__':
+    test_step_size_slope_limiter()