Reset derived quantities data

festim/exports/exports.py

@@ -136,6 +136,11 @@ def initialise_derived_quantities(self, dx, ds, materials):
         """
         for export in self:
             if isinstance(export, festim.DerivedQuantities):
+                # reset the data of the derived quantities
                 export.data = []
+                export.t = []
+                for quantity in export:
+                    quantity.t = []
+                    quantity.data = []
                 export.assign_measures_to_quantities(dx, ds)
                 export.assign_properties_to_quantities(materials)

test/system/test_misc.py

@@ -334,6 +334,33 @@ def test_materials_setter():
     assert my_model.materials is test_materials
 
 
+def test_derived_quantities_data_is_reset():
+    """
+    Checks that the data of a derived quantity is reset at each timestep
+    """
+    my_model = F.Simulation()
+
+    my_model.mesh = F.MeshFromVertices([0, 1, 2, 3, 4])
+
+    my_model.materials = F.Material(id=1, D_0=1, E_D=0)
+    my_model.T = F.Temperature(400)
+
+    left_flux = F.SurfaceFlux(field="solute", surface=1)
+
+    my_model.exports = [F.DerivedQuantities([left_flux])]
+
+    my_model.settings = F.Settings(
+        absolute_tolerance=1e-15,
+        relative_tolerance=1e-15,
+        transient=False,
+    )
+
+    for i in range(3):
+        my_model.initialise()
+        assert len(left_flux.data) == 0
+        my_model.run()
+
+
 class TestFestimProblem:
     """Tests the methods of the festim.Problem class"""