Modified Gram-Schmidt: add docu

diff --git a/doc/news/changes/minor/20221208Munch b/doc/news/changes/minor/20221208Munch
new file mode 100644 (file)
index 0000000..e90bef2
--- /dev/null
+++ b/doc/news/changes/minor/20221208Munch
@@ -0,0 +1,6 @@
+New: SolverGMRES now also supports classical Gram-Schmidt orthonormalization
+alongside to the existing modified Gram-Schmidt algorithm. This
+allows to reduce the cost of vector operations in terms of
+communication latency and memory transfer significantly.
+<br>
+(Peter Munch, Martin Kronbichler, 2022/12/08)

diff --git a/include/deal.II/lac/solver_gmres.h b/include/deal.II/lac/solver_gmres.h
index 76bc111c58cc91d65344a1ca67429978414acf33..70a3b164a1a0da5edfbe8edf66a3eae9a095ccbf 100644 (file)
--- a/include/deal.II/lac/solver_gmres.h
+++ b/include/deal.II/lac/solver_gmres.h
@@ -204,7 +204,10 @@ public:
        */
       modified_gram_schmidt,
       /**
-       * Use classical Gram-Schmidt algorithm.
+       * Use classical Gram-Schmidt algorithm. Since this approach works on
+       * multi-vectors and performs a global reduction only once, it is
+       * more efficient than the modified Gram-Schmidt algorithm.
+       * However, it might be numerically unstable.
        */
       classical_gram_schmidt
     };