Add Elasticity/Stokes using biharmonic/Laplace kernels

Co-authored-by: Alex Fikl <alexfikl@gmail.com>

Author: isuruf

doc/conf.py

@@ -96,6 +96,7 @@
     # sumpy
     "ExpansionBase": "class:sumpy.expansion.ExpansionBase",
     "ExpansionFactoryBase": "class:sumpy.expansion.ExpansionFactoryBase",
+    "ExpressionKernel": "class:sumpy.kernel.ExpressionKernel",
     "Kernel": "class:sumpy.kernel.Kernel",
     "HelmholtzKernel": "class:sumpy.kernel.HelmholtzKernel",
     "P2P": "class:sumpy.p2p.P2P",

doc/symbolic.rst

@@ -38,6 +38,11 @@ Maxwell's equations
 
 .. automodule:: pytential.symbolic.pde.maxwell
 
+Elasticity equations
+^^^^^^^^^^^^^^^^^^^^
+
+.. automodule:: pytential.symbolic.elasticity
+
 Stokes' equations
 ^^^^^^^^^^^^^^^^^
 
@@ -48,6 +53,11 @@ Scalar Beltrami equations
 
 .. automodule:: pytential.symbolic.pde.beltrami
 
+Rewriting expressions with layer potentials
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. automodule:: pytential.symbolic.pde.system_utils
+
 Internal affairs
 ----------------
 
@@ -62,3 +72,10 @@ How a symbolic operator gets executed
 .. automodule:: pytential.symbolic.execution
 
 .. automodule:: pytential.symbolic.compiler
+
+Rewriting expressions with ``IntG``\ s internals
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. automethod:: pytential.symbolic.pde.system_utils.convert_target_transformation_to_source
+.. automethod:: pytential.symbolic.pde.system_utils.rewrite_int_g_using_base_kernel
+

pyproject.toml

@@ -144,6 +144,8 @@ extend-ignore-re = [
 
 [tool.typos.default.extend-words]
 "nd" = "nd"
+# short for multi-indices
+mis = "mis"
 
 [tool.basedpyright]
 reportImplicitStringConcatenation = "none"

pytential/qbx/__init__.py

@@ -1052,9 +1052,12 @@ def get_flat_strengths_from_densities(
             places,
             sym.weights_and_area_elements(places.ambient_dim, dofdesc=dofdesc),
             )(actx)
+
+    from numbers import Number
+
     density_dofarrays = [evaluate(density) for density in densities]
     for i, ary in enumerate(density_dofarrays):
-        if not isinstance(ary, DOFArray):
+        if not isinstance(ary, DOFArray | Number):
             raise ValueError(
                 f"DOFArray expected for density '{densities[i]}', "
                 f"{type(ary)} received instead")