Add d3.random.{logNormal,irwinHall}. Fixes d3#571.

d3.v2.js

@@ -183,17 +183,33 @@
     return [ a, c ];
   };
   d3.random = {
-    normal: function(mean, deviation) {
-      if (arguments.length < 2) deviation = 1;
-      if (arguments.length < 1) mean = 0;
+    normal: function(µ, σ) {
+      var n = arguments.length;
+      if (n < 2) σ = 1;
+      if (n < 1) µ = 0;
       return function() {
         var x, y, r;
         do {
           x = Math.random() * 2 - 1;
           y = Math.random() * 2 - 1;
           r = x * x + y * y;
         } while (!r || r > 1);
-        return mean + deviation * x * Math.sqrt(-2 * Math.log(r) / r);
+        return µ + σ * x * Math.sqrt(-2 * Math.log(r) / r);
+      };
+    },
+    logNormal: function(µ, σ) {
+      var n = arguments.length;
+      if (n < 2) σ = 1;
+      if (n < 1) µ = 0;
+      var random = d3.random.normal();
+      return function() {
+        return Math.exp(µ + σ * random());
+      };
+    },
+    irwinHall: function(m) {
+      return function() {
+        for (var s = 0, j = 0; j < m; j++) s += Math.random();
+        return s / m;
       };
     }
   };

src/core/random.js

@@ -1,15 +1,31 @@
 d3.random = {
-  normal: function(mean, deviation) {
-    if (arguments.length < 2) deviation = 1;
-    if (arguments.length < 1) mean = 0;
+  normal: function(µ, σ) {
+    var n = arguments.length;
+    if (n < 2) σ = 1;
+    if (n < 1) µ = 0;
     return function() {
       var x, y, r;
       do {
         x = Math.random() * 2 - 1;
         y = Math.random() * 2 - 1;
         r = x * x + y * y;
       } while (!r || r > 1);
-      return mean + deviation * x * Math.sqrt(-2 * Math.log(r) / r);
+      return µ + σ * x * Math.sqrt(-2 * Math.log(r) / r);
+    };
+  },
+  logNormal: function(µ, σ) {
+    var n = arguments.length;
+    if (n < 2) σ = 1;
+    if (n < 1) µ = 0;
+    var random = d3.random.normal();
+    return function() {
+      return Math.exp(µ + σ * random());
+    };
+  },
+  irwinHall: function(m) {
+    return function() {
+      for (var s = 0, j = 0; j < m; j++) s += Math.random();
+      return s / m;
     };
   }
 };

test/core/random-test.js

@@ -0,0 +1,35 @@
+require("../env");
+
+var vows = require("vows"),
+    assert = require("assert");
+
+var suite = vows.describe("d3.random");
+
+suite.addBatch({
+  "normal": {
+    "topic": function() {
+      return d3.random.normal();
+    },
+    "returns a number": function(random) {
+      assert.typeOf(random(), "number");
+    }
+  },
+  "logNormal": {
+    "topic": function() {
+      return d3.random.logNormal();
+    },
+    "returns a number": function(random) {
+      assert.typeOf(random(), "number");
+    }
+  },
+  "irwinHall": {
+    "topic": function() {
+      return d3.random.irwinHall(10);
+    },
+    "returns a number": function(random) {
+      assert.typeOf(random(), "number");
+    }
+  }
+});
+
+suite.export(module);