[field] Add Field.as_boundary()

docs/Complex_Boundaries.ipynb

@@ -123,7 +123,7 @@
     {
       "cell_type": "markdown",
       "source": [
-        "Next, we define the full domain boundary. When using a `Field` as a Dirichlet boundary condition, we need to convert it using `field.as_boundary()`. For the right side, we use free flow (Neumann) and for the top and bottom, we set velocity=0."
+        "Next, we define the full domain boundary. When using a `Field` as a Dirichlet boundary condition, we need to convert it using `as_boundary()`. For the right side, we use free flow (Neumann) and for the top and bottom, we set velocity=0."
       ],
       "metadata": {
         "id": "FTr1BaPXFdVC"
@@ -132,7 +132,7 @@
     {
       "cell_type": "code",
       "source": [
-        "boundary = {'x-': field.as_boundary(inflow, None), 'x+': ZERO_GRADIENT, 'y': 0}"
+        "boundary = {'x-': inflow.as_boundary(), 'x+': ZERO_GRADIENT, 'y': 0}"
       ],
       "metadata": {
         "id": "VeZgY-liClie"

phi/field/_field.py

@@ -726,6 +726,18 @@ def grid_scatter(self, *args, **kwargs):
         from ._resample import grid_scatter
         return grid_scatter(self, *args, **kwargs)
 
+    def as_boundary(self) -> Extrapolation:
+        """
+        Returns an `Extrapolation` representing this 'Field''s values as a Dirichlet (constant) boundary.
+        If this `Field` encloses the required boundaries, its values will be interpolated to the required boundaries.
+        If boundaries outside of this `Field`'s sampled domain are required, this `Field`'s boundary conditions will be applied to determine the boundary values.
+
+        Returns:
+            `Extrapolation`
+        """
+        from ._embed import FieldEmbedding
+        return FieldEmbedding(self)
+
 
 def as_boundary(obj: Union[Extrapolation, Tensor, float, Field, None], _geometry=None) -> Extrapolation:
     """
@@ -741,11 +753,7 @@ def as_boundary(obj: Union[Extrapolation, Tensor, float, Field, None], _geometry
     Returns:
         `Extrapolation`
     """
-    if isinstance(obj, Field):
-        from ._embed import FieldEmbedding
-        return FieldEmbedding(obj)
-    else:
-        return math.extrapolation.as_extrapolation(obj)
+    return obj.as_boundary() if isinstance(obj, Field) else math.extrapolation.as_extrapolation(obj)
 
 
 def is_staggered(values: Tensor, geometry: Geometry):