Initial data commit

Task/Statistics-Normal-distribution/Racket/statistics-normal-distribution-1.rkt

@@ -0,0 +1,13 @@
+#lang racket
+(require math (planet williams/science/histogram-with-graphics))
+
+(define data (sample (normal-dist 50 4) 100000))
+
+(displayln (~a "Mean:\t"   (mean data)))
+(displayln (~a "Stddev:\t" (stddev data)))
+(displayln (~a "Max:\t"    (apply max data)))
+(displayln (~a "Min:\t"    (apply min data)))
+
+(define h (make-histogram-with-ranges-uniform 40 30 70))
+(for ([x data]) (histogram-increment! h x))
+(histogram-plot h "Normal distribution μ=50 σ=4")

Task/Statistics-Normal-distribution/Racket/statistics-normal-distribution-2.rkt

@@ -0,0 +1,19 @@
+#lang racket
+(require math)
+
+(define random-normal
+  (let ([unit (uniform-dist)]
+        [next #f])
+    (λ (μ σ)
+      (if next
+          (begin0
+            (+ μ (* σ next))
+            (set! next #f))
+          (let loop ()
+            (let* ([v1 (- (* 2.0 (sample unit)) 1.0)]
+                   [v2 (- (* 2.0 (sample unit)) 1.0)]
+                   [s (+ (sqr v1) (sqr v2))])
+              (cond [(>= s 1) (loop)]
+                    [else (define scale (sqrt (/ (* -2.0 (log s)) s)))
+                          (set! next (* scale v2))
+                          (+ μ (* σ scale v1))])))))))