Initialise Stepsize.value in Simulation.initialise()

FESTIM/generic_simulation.py

@@ -218,6 +218,11 @@ def initialise(self):
             raise AttributeError("dt must be None in steady state simulations")
         if self.settings.transient and self.dt is None:
             raise AttributeError("dt must be provided in transient simulations")
+
+        # initialise dt
+        if self.settings.transient:
+            self.dt.initialise_value()
+
         self.h_transport_problem = HTransportProblem(
             self.mobile, self.traps, self.T, self.settings, self.initial_conditions
         )
@@ -328,7 +333,7 @@ def iterate(self):
 
         # avoid t > final_time
         next_time = self.t + float(self.dt.value)
-        if next_time > self.settings.final_time:
+        if next_time > self.settings.final_time and self.t != self.settings.final_time:
             self.dt.value.assign(self.settings.final_time - self.t)
 
     def display_time(self):

FESTIM/stepsize.py

@@ -40,7 +40,14 @@ def __init__(
                 "stepsize_stop_max": stepsize_stop_max,
                 "dt_min": dt_min,
             }
-        self.value = f.Constant(initial_value, name="dt")
+        self.initial_value = initial_value
+        self.value = None
+        self.initialise_value()
+
+    def initialise_value(self):
+        """Creates a fenics.Constant object initialised with self.initial_value
+        and stores it in self.value"""
+        self.value = f.Constant(self.initial_value, name="dt")
 
     def adapt(self, t, nb_it, converged):
         """Changes the stepsize based on convergence.

Tests/simulation/test_initialise.py

@@ -49,3 +49,25 @@ def test_initialise_sets_t_to_zero():
 
     # check that my_model.t is reinitialised to zero
     assert my_model.t == 0
+
+
+def test_initialise_initialise_dt():
+    """Creates a Simulation object and checks that .initialise() sets
+    the value attribute of the dt attribute to dt.initial_value
+    """
+    # build
+    my_model = F.Simulation()
+    my_model.mesh = F.MeshFromVertices([1, 2, 3])
+    my_model.materials = F.Material(id=1, D_0=1, E_D=0, thermal_cond=1)
+    my_model.T = F.Temperature(100)
+    my_model.dt = F.Stepsize(initial_value=3)
+    my_model.settings = F.Settings(
+        absolute_tolerance=1e-10, relative_tolerance=1e-10, final_time=4
+    )
+    my_model.dt.value.assign(26)
+
+    # run
+    my_model.initialise()
+
+    # test
+    assert my_model.dt.value(2) == 3