copy from scripts/linear-algebra/krylovb.m
copy to scripts/deprecated/krylovb.m
--- a/scripts/linear-algebra/krylovb.m
+++ b/scripts/deprecated/krylovb.m
@@ -21,8 +21,17 @@
 ## See @code{krylov}.
 ## @end deftypefn
 
+## Deprecated in version 3.4
+
 function [Uret, Ucols] = krylovb (A, V, k, eps1, pflg)
 
+  persistent warned = false;
+  if (! warned)
+    warned = true;
+    warning ("Octave:deprecated-function",
+             "krylovb is obsolete and will be removed from a future version of Octave; please use [Uret, ~, Ucols] = krylov (...) instead");
+  endif
+
   switch (nargin)
     case (3)
       [Uret, H, Ucols] = krylov (A, V, k);