Data commit

Task/Random-numbers/Erlang/random-numbers.erl

@@ -0,0 +1,31 @@
+mean(Values) ->
+    mean(tl(Values), hd(Values), 1).
+
+mean([], Acc, Length) ->
+    Acc / Length;
+mean(Values, Acc, Length) ->
+    mean(tl(Values), hd(Values)+Acc, Length+1).
+
+variance(Values) ->
+    Mean = mean(Values),
+    variance(Values, Mean, 0) / length(Values).
+
+variance([], _, Acc) ->
+    Acc;
+variance(Values, Mean, Acc) ->
+    Diff = hd(Values) - Mean,
+    DiffSqr = Diff * Diff,
+    variance(tl(Values), Mean, Acc + DiffSqr).
+
+stddev(Values) ->
+    math:sqrt(variance(Values)).
+
+normal(Mean, StdDev) ->
+    U = random:uniform(),
+    V = random:uniform(),
+    Mean + StdDev * ( math:sqrt(-2 * math:log(U)) * math:cos(2 * math:pi() * V) ).  % Erlang's math:log is the natural logarithm.
+
+main(_) ->
+    X = [ normal(1.0, 0.5) || _ <- lists:seq(1, 1000) ],
+    io:format("mean = ~w\n", [mean(X)]),
+    io:format("stddev = ~w\n", [stddev(X)]).