From b601d154c16011b6aa25432ee2ab0f34711e28d9 Mon Sep 17 00:00:00 2001
From: John Benediktsson <mrjbq7@gmail.com>
Date: Tue, 25 Sep 2012 10:48:09 -0700
Subject: [PATCH] math.extras: fix spelling of stirling, add ramanujan
approximation of factorial.
---
extra/math/extras/extras-docs.factor | 2 +-
extra/math/extras/extras.factor | 17 ++++++++++-------
2 files changed, 11 insertions(+), 8 deletions(-)
diff --git a/extra/math/extras/extras-docs.factor b/extra/math/extras/extras-docs.factor
index e745caa3d1..93200cea81 100644
--- a/extra/math/extras/extras-docs.factor
+++ b/extra/math/extras/extras-docs.factor
@@ -9,7 +9,7 @@ HELP: bernoulli
{ $values { "p" integer } { "n" rational } }
{ $description "Return the Bernoulli number " { $snippet "p" } "." } ;
-HELP: sterling
+HELP: stirling
{ $values { "n" integer } { "k" integer } { "x" integer } }
{ $description "Return the Stirling number of the second kind for a set with " { $snippet "n" } " elements partitioned into " { $snippet "k" } " disjoint non-empty sets." } ;
diff --git a/extra/math/extras/extras.factor b/extra/math/extras/extras.factor
index f3f6cea307..74e27c7a18 100644
--- a/extra/math/extras/extras.factor
+++ b/extra/math/extras/extras.factor
@@ -1,7 +1,7 @@
! Copyright (C) 2012 John Benediktsson
! See http://factorcode.org/license.txt for BSD license
-USING: combinators.short-circuit grouping kernel math
+USING: combinators.short-circuit grouping kernel locals math
math.combinatorics math.constants math.functions math.order
math.primes math.ranges math.statistics math.vectors memoize
sequences ;
@@ -10,18 +10,21 @@ IN: math.extras
<PRIVATE
-DEFER: sterling
+DEFER: stirling
-: (sterling) ( n k -- x )
- [ [ 1 - ] bi@ sterling ]
- [ [ 1 - ] dip sterling ]
+: (stirling) ( n k -- x )
+ [ [ 1 - ] bi@ stirling ]
+ [ [ 1 - ] dip stirling ]
[ nip * + ] 2tri ;
PRIVATE>
-MEMO: sterling ( n k -- x )
+MEMO: stirling ( n k -- x )
2dup { [ = ] [ nip 1 = ] } 2||
- [ 2drop 1 ] [ (sterling) ] if ;
+ [ 2drop 1 ] [ (stirling) ] if ;
+
+:: ramanujan ( x -- y )
+ pi sqrt x e / x ^ * x 8 * 4 + x * 1 + x * 1/30 + 1/6 ^ * ;
<PRIVATE