Merge pull request #700 from zwicker-group/test_mixed_derivatives

Add tests for mixed derivatives in Cartesian and cylindrical grids

Author: david-zwicker

pde/fields/base.py

@@ -636,15 +636,15 @@ def apply(
         Args:
             func (callable or str):
                 The (vectorized) function being applied to the data or an expression
-                that can be parsed using sympy (:func:`~pde.tools.expression.evaluate`
+                that can be parsed using sympy (:func:`~pde.tools.expressions.evaluate`
                 is used in this case). The local field values can be accessed using the
                 field labels for a field collection and via the variable `c` otherwise.
             out (FieldBase, optional):
                 Optional field into which the data is written
             label (str, optional):
                 Name of the returned field
             evaluate_args (dict):
-                Additional arguments passed to :func:`~pde.tools.expression.evaluate`.
+                Additional arguments passed to :func:`~pde.tools.expressions.evaluate`.
                 Only used when `func` is a string.
 
         Returns:
@@ -660,7 +660,10 @@ def apply(
             if evaluate_args is None:
                 evaluate_args = {}
             if isinstance(self, DataFieldBase):
-                result = evaluate(func, {"c": self}, **evaluate_args)
+                fields = {"c": self}
+                if self.label is not None:
+                    fields[self.label] = self
+                result = evaluate(func, fields, **evaluate_args)
             elif isinstance(self, FieldCollection):
                 result = evaluate(func, self, **evaluate_args)
             else:

tests/grids/test_cartesian_grids.py

@@ -353,3 +353,14 @@ def test_9point_stencil(periodic, corner_weight):
     reference = field.laplace(bc="auto_periodic_neumann")
     test = field.laplace(bc="auto_periodic_neumann", corner_weight=corner_weight)
     np.testing.assert_allclose(reference.data, test.data, atol=corner_weight / 3)
+
+
+@pytest.mark.parametrize("periodic", [True, False])
+def test_mixed_derivatives(periodic):
+    """Test mixed derivatives of scalar fields."""
+    grid = CartesianGrid([[0, 1], [-1, 0.5]], [7, 9], periodic=periodic)
+    field = ScalarField.random_normal(grid, label="fld")
+
+    res1 = field.apply("d_dx(d_dy(fld))")
+    res2 = field.apply("d_dy(d_dx(fld))")
+    np.testing.assert_allclose(res1.data, res2.data)

tests/grids/test_cylindrical_grids.py

@@ -77,3 +77,13 @@ def test_setting_boundary_conditions():
     grid.get_boundary_conditions({"r": "derivative", "z": "periodic"})
     with pytest.raises(RuntimeError):
         grid.get_boundary_conditions({"r": "derivative", "z": "derivative"})
+
+
+def test_mixed_derivatives():
+    """Test mixed derivatives of scalar fields."""
+    grid = CylindricalSymGrid(1, [-1, 0.5], [7, 9])
+    field = ScalarField.random_normal(grid, label="c")
+
+    res1 = field.apply("d_dz(d_dr(c))")
+    res2 = field.apply("d_dr(d_dz(c))")
+    np.testing.assert_allclose(res1.data, res2.data)