From: Wolfgang Bangerth <bangerth@colostate.edu>
Date: Tue, 17 Jan 2023 22:03:49 +0000 (-0700)
Subject: Add a comment for a recent patch.
X-Git-Tag: v9.5.0-rc1~633^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b4b41da1d232a192f023fce3adc07f76cd977e53;p=dealii.git

Add a comment for a recent patch.
---

diff --git a/source/grid/grid_reordering.cc b/source/grid/grid_reordering.cc
index 7e37ecd9f1..d61d72ada7 100644
--- a/source/grid/grid_reordering.cc
+++ b/source/grid/grid_reordering.cc
@@ -32,17 +32,23 @@ DEAL_II_NAMESPACE_OPEN
 namespace
 {
   /**
-   * A set of functions that
-   * reorder the data from the
-   * "current" to the "classic"
-   * format of vertex numbering of
-   * cells and faces. These functions
-   * do the reordering of their
-   * arguments in-place.
+   * This file uses a different ordering for the vertices in a hex
+   * cell than we usually do in deal.II. The different convention used
+   * here originates in what we believed the ordering to be in UCD
+   * format, until it was discovered in 2022 that UCD will interpret
+   * this ordering to correspond to inverted cells -- as a
+   * consequence, the UCD ordering was fixed, but the current file is
+   * stuck on the old ordering.
    */
   constexpr std::array<unsigned int, 8> local_vertex_numbering{
     {0, 1, 5, 4, 2, 3, 7, 6}};
 
+  /**
+   * Following is a set of functions that reorder the data from the
+   * "current" to the "classic" format of vertex numbering of cells
+   * and faces. These functions do the reordering of their arguments
+   * in-place.
+   */
   void
   reorder_new_to_old_style(std::vector<CellData<1>> &)
   {}