test case that uses ramanujan's series for approximating pi

tests/more-tests/ramanujan-pi.expected

@@ -0,0 +1 @@
+3.1415926535897927

tests/more-tests/ramanujan-pi.rkt

@@ -0,0 +1,35 @@
+#lang planet dyoo/whalesong
+;; Srinivasa Ramanujan's infinite series for approximating pi.
+
+(define (sum f a b)
+  (cond
+    [(= a b)
+     (f a)]
+    [else
+     (+ (f a)
+        (sum f (add1 a) b))]))
+
+(define (fact x)
+  (cond
+    [(= x 0)
+     1]
+    [else
+     (* x (fact (sub1 x)))]))
+
+
+(define (1/pi-approx n)
+  (* (/ (* 2 (sqrt 2))
+        9801)
+     (sum (lambda (k)
+            (/ (* (fact (* 4 k))
+                  (+ 1103 (* 26390 k)))
+               (* (expt (fact k) 4)
+                  (expt 396 (* 4 k)))))
+          0
+          n)))
+
+(define (pi-approx n)
+  (/ 1 (1/pi-approx n)))
+
+
+(pi-approx 10)

tests/run-more-tests.rkt

@@ -52,3 +52,4 @@
 (test "more-tests/scheme-whalesong.rkt")
 (test "more-tests/nestedloop.rkt")
 (test "more-tests/nucleic2.rkt")
+(test "more-tests/ramanujan-pi.rkt")