IMEX version of the polynomial test problem

pySDC/implementations/problem_classes/polynomial_test_problem.py

@@ -1,7 +1,7 @@
 import numpy as np
 
 from pySDC.core.Problem import ptype
-from pySDC.implementations.datatype_classes.mesh import mesh
+from pySDC.implementations.datatype_classes.mesh import mesh, imex_mesh
 
 
 class polynomial_testequation(ptype):
@@ -88,3 +88,35 @@ def u_exact(self, t, **kwargs):
         me = self.dtype_u(self.init)
         me[:] = self.poly(t)
         return me
+
+
+class polynomial_testequation_IMEX(polynomial_testequation):
+    """
+    IMEX version of the polynomial test problem that assigns half the derivative to the implicit part and the other half to the explicit part.
+    Keep in mind that you still cannot Really perform any solves.
+    """
+
+    dtype_f = imex_mesh
+
+    def eval_f(self, u, t):
+        """
+        Derivative of the polynomial.
+
+        Parameters
+        ----------
+        u : dtype_u
+            Current values of the numerical solution.
+        t : float
+            Current time of the numerical solution is computed.
+
+        Returns
+        -------
+        f : dtype_f
+            The right-hand side of the problem.
+        """
+
+        f = self.dtype_f(self.init)
+        derivative = self.poly.deriv(m=1)(t)
+        f.impl[:] = derivative / 2
+        f.expl[:] = derivative / 2
+        return f

pySDC/tests/test_convergence_controllers/test_extrapolation_within_Q.py

@@ -1,7 +1,7 @@
 import pytest
 
 
-def get_controller(dt, num_nodes, quad_type, useMPI, **kwargs):
+def get_controller(dt, num_nodes, quad_type, useMPI, imex, **kwargs):
     """
     Gets a controller setup for the polynomial test problem.
 
@@ -10,17 +10,26 @@ def get_controller(dt, num_nodes, quad_type, useMPI, **kwargs):
         num_nodes (int): Number of nodes
         quad_type (str): Type of quadrature
         useMPI (bool): Whether or not to use MPI
+        imex (bool): Use IMEX version of the test problem
 
     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
     from pySDC.implementations.controller_classes.controller_nonMPI import controller_nonMPI
     from pySDC.implementations.convergence_controller_classes.estimate_extrapolation_error import (
         EstimateExtrapolationErrorWithinQ,
     )
 
+    if imex:
+        from pySDC.implementations.problem_classes.polynomial_test_problem import (
+            polynomial_testequation_IMEX as problem_class,
+        )
+    else:
+        from pySDC.implementations.problem_classes.polynomial_test_problem import (
+            polynomial_testequation as problem_class,
+        )
+
     if useMPI:
         from pySDC.implementations.sweeper_classes.generic_implicit_MPI import generic_implicit_MPI as sweeper_class
         from mpi4py import MPI
@@ -55,7 +64,7 @@ def get_controller(dt, num_nodes, quad_type, useMPI, **kwargs):
 
     # fill description dictionary for easy step instantiation
     description = {}
-    description['problem_class'] = polynomial_testequation
+    description['problem_class'] = problem_class
     description['problem_params'] = problem_params
     description['sweeper_class'] = sweeper_class
     description['sweeper_params'] = sweeper_params
@@ -179,6 +188,7 @@ def test_extrapolation_within_Q(num_nodes, quad_type):
         'quad_type': quad_type,
         'useMPI': False,
         'QI': 'MIN',
+        'imex': False,
     }
 
     import numpy as np
@@ -219,5 +229,6 @@ def test_extrapolation_within_Q_MPI(num_nodes, quad_type):
             'quad_type': sys.argv[2],
             'useMPI': True,
             'QI': 'MIN',
+            'imex': True,
         }
         check_order([5e-1, 1e-1, 8e-2, 5e-2], **kwargs)