Merge pull request festim-dev#1028 from jhdark/cov_fix

[BUG] Fix for exports with Change of Variable method

Author: RemDelaporteMathurin

src/festim/exports/vtx.py

@@ -162,7 +162,7 @@ def get_functions(self) -> list[fem.Function]:
                 legacy_output = True
                 break
         if legacy_output:
-            return [field.sub_function for field in self._field]
+            return [field.post_processing_solution for field in self._field]
         else:
             if self._subdomain is None:
                 raise ValueError("Subdomain must be specified")

test/test_vtx.py

@@ -14,7 +14,7 @@ def test_vtx_export_one_function(tmpdir):
     """Test can add one function to a vtx export"""
     u = dolfinx.fem.Function(V)
     sp = F.Species("H")
-    sp.sub_function = u
+    sp.post_processing_solution = u
     filename = str(tmpdir.join("my_export.bp"))
     my_export = F.VTXSpeciesExport(filename, field=sp)
 
@@ -30,8 +30,8 @@ def test_vtx_export_two_functions(tmpdir):
 
     sp1 = F.Species("1")
     sp2 = F.Species("2")
-    sp1.sub_function = u
-    sp2.sub_function = v
+    sp1.post_processing_solution = u
+    sp2.post_processing_solution = v
     filename = str(tmpdir.join("my_export.bp"))
     my_export = F.VTXSpeciesExport(filename, field=[sp1, sp2])