Document transpose data storate for blocked elements (#3156)

* Add dof transformation docs * Doc updates * correct (?) and document transpose data storage for blocked elements * that's a permutation not a transformation * Update cpp/dolfinx/fem/FiniteElement.h * Update cpp/dolfinx/fem/FiniteElement.h * better doc --------- Co-authored-by: Garth N. Wells <gnw20@cam.ac.uk>
FEniCS · Apr 22, 2024 · 91d3bee · 91d3bee
1 parent e520be2
commit 91d3bee
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Showing 2 changed files with 7 additions and 3 deletions.
diff --git a/cpp/dolfinx/fem/FiniteElement.cpp b/cpp/dolfinx/fem/FiniteElement.cpp
@@ -617,7 +617,7 @@ FiniteElement<T>::dof_permutation_fn(bool inverse, bool scalar_element) const
     }
     else if (!scalar_element)
     {
-      // Vector element
+      // Blocked element
       std::function<void(std::span<std::int32_t>, std::uint32_t)>
           sub_element_function = _sub_elements[0]->dof_permutation_fn(inverse);
       int dim = _sub_elements[0]->space_dimension();

diff --git a/cpp/dolfinx/fem/FiniteElement.h b/cpp/dolfinx/fem/FiniteElement.h
@@ -336,7 +336,7 @@ class FiniteElement
       }
       else if (!scalar_element)
       {
-        // Vector element
+        // Blocked element
         std::function<void(std::span<U>, std::span<const std::uint32_t>,
                            std::int32_t, int)>
             sub_function
@@ -438,7 +438,11 @@ class FiniteElement
       }
       else if (!scalar_element)
       {
-        // Vector element
+        // Blocked element
+        // The transformation from the left can be used here as blocked
+        // elements use xyzxyzxyz ordering, and so applying the DOF
+        // transformation from the right is equivalent to applying the DOF
+        // transformation from the left to data using xxxyyyzzz ordering
         std::function<void(std::span<U>, std::span<const std::uint32_t>,
                            std::int32_t, int)>
             sub_function