Add comment about an if

diff --git a/include/deal.II/base/index_set.h b/include/deal.II/base/index_set.h
index f4e6dfe24ac884dd23179b9f67fc77297a872418..ef6a55d575032385632ddaca62e5f5af36a587e5 100644 (file)
--- a/include/deal.II/base/index_set.h
+++ b/include/deal.II/base/index_set.h
@@ -1693,6 +1693,11 @@ IndexSet::add_indices(const ForwardIterator &begin, const ForwardIterator &end)
 
       tmp_ranges.emplace_back(begin_index, end_index);
       p = q;
+
+      // if the starting index of the next go-around of the for loop is less
+      // than the end index of the one just identified, then we will have at
+      // least one pair of ranges that are not sorted, and consequently the
+      // whole collection of ranges is not sorted.
       if (p != end && *p < end_index)
         ranges_are_sorted = false;
     }