Merge pull request #399 from firedrakeproject/timestepping_physics

PR #399: Evaluate physics at each stage of multistep methods

gusto/time_discretisation.py

@@ -373,10 +373,14 @@ def solve_stage(self, x_in, stage):
             self.x1.assign(self.x_out)
 
         elif stage == 1:
+            for evaluate in self.evaluate_source:
+                evaluate(self.x1, self.dt)
             self.solver.solve()
             self.x1.assign(0.75*x_in + 0.25*self.x_out)
 
         elif stage == 2:
+            for evaluate in self.evaluate_source:
+                evaluate(self.x1, self.dt)
             self.solver.solve()
             self.x1.assign((1./3.)*x_in + (2./3.)*self.x_out)
 
@@ -470,16 +474,22 @@ def solve_stage(self, x_in, stage):
             self.x1.assign(x_in + 0.5 * self.dt * self.k1)
 
         elif stage == 1:
+            for evaluate in self.evaluate_source:
+                evaluate(self.x1, self.dt)
             self.solver.solve()
             self.k2.assign(self.x_out)
             self.x1.assign(x_in + 0.5 * self.dt * self.k2)
 
         elif stage == 2:
+            for evaluate in self.evaluate_source:
+                evaluate(self.x1, self.dt)
             self.solver.solve()
             self.k3.assign(self.x_out)
             self.x1.assign(x_in + self.dt * self.k3)
 
         elif stage == 3:
+            for evaluate in self.evaluate_source:
+                evaluate(self.x1, self.dt)
             self.solver.solve()
             self.k4.assign(self.x_out)
             self.x1.assign(x_in + 1/6 * self.dt * (self.k1 + 2*self.k2 + 2*self.k3 + self.k4))
@@ -538,6 +548,8 @@ def solve_stage(self, x_in, stage):
             self.x1.assign(self.x_out)
 
         elif stage == 1:
+            for evaluate in self.evaluate_source:
+                evaluate(self.x1, self.dt)
             self.solver.solve()
             self.x1.assign(0.5 * x_in + 0.5 * (self.x_out))
 

integration-tests/physics/test_instant_rain.py

@@ -32,6 +32,8 @@ def run_instant_rain(dirname):
     fexpr = Constant(0)
 
     # Equation
+    # TODO: This should become a CoupledAdvectionEquation. Currently we set u
+    # and D to 0 in the ShallowWaterEquations so they do not evolve.
     vapour = WaterVapour(name="water_vapour", space='DG')
     rain = Rain(name="rain", space="DG",
                 transport_eqn=TransportEquationType.no_transport)
@@ -46,17 +48,17 @@ def run_instant_rain(dirname):
                               dumplist=['vapour', "rain"])
     diagnostic_fields = [CourantNumber()]
     io = IO(domain, output, diagnostic_fields=diagnostic_fields)
-    transport_method = DGUpwind(eqns, "water_vapour")
+    transport_method = [DGUpwind(eqns, "water_vapour")]
 
     # Physics schemes
     # define saturation function
     saturation = Constant(0.5)
     physics_schemes = [(InstantRain(eqns, saturation, rain_name="rain"),
-                        ForwardEuler(domain))]
+                        RK4(domain))]
 
     # Time stepper
-    stepper = PrescribedTransport(eqns, RK4(domain), io, transport_method,
-                                  physics_schemes=physics_schemes)
+    stepper = SplitPhysicsTimestepper(eqns, RK4(domain), io, transport_method,
+                                      physics_schemes=physics_schemes)
 
     # ------------------------------------------------------------------------ #
     # Initial conditions
@@ -76,8 +78,8 @@ def run_instant_rain(dirname):
     VD = FunctionSpace(mesh, "DG", 1)
     initial_vapour = Function(VD).interpolate(vapour_expr)
 
-    # define expected solutions; vapour should be equal to saturation and rain
-    # should be (initial vapour - saturation)
+    # TODO: This test is based on the assumption that final vapour should be
+    # equal to saturation, which might not be true when timestepping physics.
     vapour_true = Function(VD).interpolate(saturation)
     rain_true = Function(VD).interpolate(vapour0 - saturation)
 
@@ -96,16 +98,16 @@ def test_instant_rain_setup(tmpdir):
     r = stepper.fields("rain")
 
     # check that the maximum of the vapour field is equal to the saturation
-    assert v.dat.data.max() - saturation.values() < 0.001, "The maximum of the final vapour field should be equal to saturation"
+    assert v.dat.data.max() - saturation.values() < 0.1, "The maximum of the final vapour field should be equal to saturation"
 
     # check that the minimum of the vapour field hasn't changed
-    assert v.dat.data.min() - initial_vapour.dat.data.min() < 0.001, "The minimum of the vapour field should not change"
+    assert v.dat.data.min() - initial_vapour.dat.data.min() < 0.1, "The minimum of the vapour field should not change"
 
     # check that the maximum of the excess vapour agrees with the maximum of the
     # rain
     VD = Function(v.function_space())
     excess_vapour = Function(VD).interpolate(initial_vapour - saturation)
-    assert excess_vapour.dat.data.max() - r.dat.data.max() < 0.001
+    assert excess_vapour.dat.data.max() - r.dat.data.max() < 0.1
 
     # check that the minimum of the rain is 0
     assert r.dat.data.min() < 1e-8