--- a/Integer.st	Fri Jan 16 14:55:49 2009 +0100
+++ b/Integer.st	Fri Jan 16 17:22:32 2009 +0100
@@ -2147,6 +2147,7 @@
 ! !
 
 
+
 !Integer methodsFor:'misc math'!
 
 acker:n
@@ -2165,6 +2166,55 @@
     "Modified: 18.7.1996 / 13:08:16 / cg"
 !
 
+binomialCoefficient:kIn
+    |k acc|
+
+    "computes the binomialCoefficient C(n,k)
+      / n \     with self being n, and 0 <= k <= n.
+      \ k /
+
+     The binCo is defined as:
+        n!! 
+     ----------
+     k!! (n-k)!!
+
+     but there is a faster, recursive formula:
+
+      / n \  = / n - 1 \  + / n - 1 \ 
+      \ k /    \ k - 1 /    \   k   /
+
+     with:
+
+      / n \  = / n \  =  1 
+      \ 0 /    \ n /    
+    "
+
+    kIn > self ifTrue:[^ 0].
+
+    k := kIn.
+    k > (self / 2) ifTrue:[
+        "/ symmetry
+        k := self - k.
+    ].
+
+    acc := 1.
+    1 to:k do:[:i |
+        acc := acc * (self - k + i) / i.
+    ].
+    ^ acc
+
+    "
+     (7 binomialCoefficient:3)  
+     (10 binomialCoefficient:5)
+     (100 binomialCoefficient:5)
+     (1000 binomialCoefficient:5)
+     TestCase assert: (10 binomialCoefficient:5) = (10 factorial / (5 factorial * 5 factorial))
+     TestCase assert: (100 binomialCoefficient:78) = (100 factorial / (78 factorial * (100-78) factorial)) 
+     TestCase assert: (1000 binomialCoefficient:5) = (1000 factorial / (5 factorial * (1000-5) factorial)) 
+     TestCase assert: (10000 binomialCoefficient:78) = (10000 factorial / (78 factorial * (10000-78) factorial)) 
+    "
+!
+
 divMod:aNumber
     "return an array filled with self // aNumber and
      self \\ aNumber. 
@@ -3534,7 +3584,7 @@
 !Integer class methodsFor:'documentation'!
 
 version
-    ^ '$Header: /cvs/stx/stx/libbasic/Integer.st,v 1.202 2009-01-16 11:33:08 cg Exp $'
+    ^ '$Header: /cvs/stx/stx/libbasic/Integer.st,v 1.203 2009-01-16 16:22:32 cg Exp $'
 ! !
 
 Integer initialize!