math.extras: adding exponential-index.

2012-09-26 15:29:08 -07:00 · 2012-09-26 15:29:08 -07:00 · 1fe94e4184
parent 30382dbf4a
commit 1fe94e4184
1 changed files with 3 additions and 0 deletions
--- a/extra/math/extras/extras.factor
+++ b/extra/math/extras/extras.factor
@ -185,3 +185,6 @@ PRIVATE>
 : normalized-herfindahl ( seq -- x )
    [ herfindahl ] [ length recip ] bi
    [ - ] [ 1 swap - / ] bi ;
+
+: exponential-index ( seq -- x )
+    dup sum '[ _ / dup ^ ] map-product ;