2014-12-02: make H linear with position.

make H linear with position.

diff --git a/examples/ensemble-estimation.w b/examples/ensemble-estimation.w
--- a/examples/ensemble-estimation.w
+++ b/examples/ensemble-estimation.w
@@ -101,7 +101,7 @@ x are parameters to be optimized, pos is
            apply +
                  list-ec (: i len)
                       * : list-ref x i
-                          expt pos 2
+                          . pos
                           exp 
                             - 
                               / : expt {pos - (list-ref x-pos i)} 2