Merge branch 'fem_dev' into 'main'

warp.fem: Variable nodes per element, global lookups, 3d streamlines example

See merge request omniverse/warp!554

CHANGELOG.md

@@ -25,6 +25,12 @@
   - Sparse matrix allocations (from `bsr_from_triplets`, `bsr_axpy`, etc) can now be captured in CUDA graphs; exact number of non-zeros can be optionally requested asynchronously.
   - `bsr_assign` now supports changing block shape (including CSR/BSR conversions)
   - Add Python operator overloads for common sparse matrix operations, e.g `A += 0.5 * B`, `y = x @ C`
+- `warp.fem` new features and fixes:
+  - Support for variable number of nodes per element
+  - Global `wp.fem.lookup()` operator now supports `wp.fem.Tetmesh` and `wp.fem.Trimesh2D` geometries
+  - Simplified defining custom subdomains (`wp.fem.Subdomain`), free-slip boundary conditions
+  - New `streamlines` example, updated `mixed_elasticity` to use a nonlinear model
+  - Fixed edge cases with Nanovdb function spaces
 
 ## [1.2.1] - 2024-06-14
 

README.md

@@ -149,28 +149,28 @@ Built-in unit tests can be run from the command-line as follows:
 <table>
     <tbody>
         <tr>
-            <td><a href="https://github.com/NVIDIA/warp/tree/main/warp/examples/fem/example_apic_fluid.py"><img src="https://github.com/NVIDIA/warp/raw/main/docs/img/examples/fem_apic_fluid.png"></a></td>
-            <td><a href="https://github.com/NVIDIA/warp/tree/main/warp/examples/fem/example_convection_diffusion.py"><img src="https://github.com/NVIDIA/warp/raw/main/docs/img/examples/fem_convection_diffusion.png"></a></td>
             <td><a href="https://github.com/NVIDIA/warp/tree/main/warp/examples/fem/example_diffusion_3d.py"><img src="https://github.com/NVIDIA/warp/raw/main/docs/img/examples/fem_diffusion_3d.png"></a></td>
-            <td><a href="https://github.com/NVIDIA/warp/tree/main/warp/examples/fem/example_diffusion.py"><img src="https://github.com/NVIDIA/warp/raw/main/docs/img/examples/fem_diffusion.png"></a></td>
+            <td><a href="https://github.com/NVIDIA/warp/tree/main/warp/examples/fem/example_mixed_elasticity.py"><img src="https://github.com/NVIDIA/warp/raw/main/docs/img/examples/fem_mixed_elasticity.png"></a></td>
+            <td><a href="https://github.com/NVIDIA/warp/tree/main/warp/examples/fem/example_apic_fluid.py"><img src="https://github.com/NVIDIA/warp/raw/main/docs/img/examples/fem_apic_fluid.png"></a></td>
+            <td><a href="https://github.com/NVIDIA/warp/tree/main/warp/examples/fem/example_streamlines.py"><img src="https://github.com/NVIDIA/warp/raw/main/docs/img/examples/fem_streamlines.png"></a></td>
         </tr>
         <tr>
-            <td align="center">apic fluid</td>
-            <td align="center">convection diffusion</td>
             <td align="center">diffusion 3d</td>
-            <td align="center">diffusion</td>
+            <td align="center">mixed elasticity</td>
+            <td align="center">apic fluid</td>
+            <td align="center">streamlines</td>
         </tr>
         <tr>
-            <td><a href="https://github.com/NVIDIA/warp/tree/main/warp/examples/fem/example_mixed_elasticity.py"><img src="https://github.com/NVIDIA/warp/raw/main/docs/img/examples/fem_mixed_elasticity.png"></a></td>
+            <td><a href="https://github.com/NVIDIA/warp/tree/main/warp/examples/fem/example_convection_diffusion.py"><img src="https://github.com/NVIDIA/warp/raw/main/docs/img/examples/fem_convection_diffusion.png"></a></td>
             <td><a href="https://github.com/NVIDIA/warp/tree/main/warp/examples/fem/example_navier_stokes.py"><img src="https://github.com/NVIDIA/warp/raw/main/docs/img/examples/fem_navier_stokes.png"></a></td>
-            <td><a href="https://github.com/NVIDIA/warp/tree/main/warp/examples/fem/example_stokes_transfer.py"><img src="https://github.com/NVIDIA/warp/raw/main/docs/img/examples/fem_stokes_transfer.png"></a></td>
-            <td><a href="https://github.com/NVIDIA/warp/tree/main/warp/examples/fem/example_stokes.py"><img src="https://github.com/NVIDIA/warp/raw/main/docs/img/examples/fem_stokes.png"></a></td>
+            <td><a href="https://github.com/NVIDIA/warp/tree/main/warp/examples/fem/example_burgers.py"><img src="https://github.com/NVIDIA/warp/raw/main/docs/img/examples/fem_burgers.png"></a></td>
+            <td><a href="https://github.com/NVIDIA/warp/tree/main/warp/examples/fem/example_deformed_geometry.py"><img src="https://github.com/NVIDIA/warp/raw/main/docs/img/examples/fem_deformed_geometry.png"></a></td>
         </tr>
         <tr>
-            <td align="center">mixed elasticity</td>
+            <td align="center">convection diffusion</td>
             <td align="center">navier stokes</td>
-            <td align="center">stokes transfer</td>
-            <td align="center">stokes</td>
+            <td align="center">burgers</td>
+            <td align="center">deformed geometry</td>
         </tr>
     </tbody>
 </table>

docs/modules/fem.rst

@@ -19,9 +19,11 @@ The main mechanism is the :py:func:`.integrand` decorator, for instance: ::
     @integrand
     def linear_form(
         s: Sample,
+        domain: Domain,
         v: Field,
     ):
-        return v(s)
+        x = domain(s)
+        return v(s) * wp.max(0.0, 1.0 - wp.length(x))
 
 
     @integrand
@@ -31,7 +33,7 @@ The main mechanism is the :py:func:`.integrand` decorator, for instance: ::
             grad(v, s),
         )
 
-Integrands are normal Warp kernels, meaning any usual Warp function can be used. 
+Integrands are normal Warp kernels, meaning that they may contain arbitrary Warp functions. 
 However, they accept a few special parameters:
 
   - :class:`.Sample` contains information about the current integration sample point, such as the element index and coordinates in element.
@@ -123,7 +125,8 @@ Introductory examples
  - ``example_burgers.py``: 2D inviscid Burgers using Discontinuous Galerkin with upwind transport and slope limiter
  - ``example_stokes.py``: 2D incompressible Stokes flow using mixed :math:`P_k/P_{k-1}` or :math:`Q_k/P_{(k-1)d}` elements
  - ``example_navier_stokes.py``: 2D Navier-Stokes flow using mixed :math:`P_k/P_{k-1}` elements
- - ``example_mixed_elasticity.py``: 2D linear elasticity using mixed continuous/discontinuous :math:`S_k/P_{(k-1)d}` elements
+ - ``example_mixed_elasticity.py``: 2D nonlinear elasticity using mixed continuous/discontinuous :math:`S_k/P_{(k-1)d}` elements
+ - ``example_streamlines.py``: Using the :func:`lookup` operator to trace through a velocity field
 
 
 Advanced usages
@@ -269,6 +272,9 @@ Geometry
 .. autoclass:: FrontierSides
    :show-inheritance:
 
+.. autoclass:: Subdomain
+   :show-inheritance:
+
 .. autoclass:: Polynomial
    :members: