Added centroid static method

README.md

@@ -4,6 +4,11 @@ Mathware
 A small compact library for algebra and vector manipulation for Node.js.
 Tries to be small and have no dependencies.
 
+## Note
+The library is permissive on purpose. It won't check a v2 vs a v3 sum. 
+It is on purpose to avoid the performance penalty hit.
+
+I'll add soon JSDoc so at least you have those checks upfront. 
 
 Download
 --------
@@ -40,7 +45,7 @@ You can also create with a shorthand
 var v3 = mw.v3(1.0, 2.0, 3.0); // Vec3 {x:1 , y:2, z:3 }
 ```
 
-Document
+Documentation
 --------
 
 You can select the vector modules out for your need
@@ -66,6 +71,16 @@ var aNewVector = mw.vec3.add(v1, v2);
 // v1{ 1,1,1} , v2{ 0,0, 1}, aNewVector {1,1,2}
 ```
 
+## Chaining 
+
+All the in place methods that should return a vector, will return this
+```js
+var v1 = mw.v2(1,2)
+        .scalarMultiply(2)
+        .add( mw.v2(-2, -2) );
+//v1 { x: 0, y : 2 }
+```
+
 ### Instance Methods ###
 
 **constructor** 
@@ -123,4 +138,18 @@ Compares the two vectors and returns true if equal
 
 ### Static Methods ###
 
-There is a static method version for every instance method that return a vector.
+There is a static method version for every instance method that return a vector. also 
+
+**centroid(ary)**
+
+Returns the centroid of an array of vectors 
+
+```js
+//Define a square of 10x10
+let v1 = mw.v2(0,0);
+let v2 = mw.v2(10,10);
+let v3 = mw.v2(0,10);
+let v4 = mw.v2(10,0);
+console.dir(mw.vec2.centroid([v1,v2,v3,v4])); // {x:5, y:5}
+```
+

lib/vec2.js

@@ -146,6 +146,13 @@ class Vec2 {
         return v1.squaredDistance(v2);
     }
 
+    static centroid(vectors) {
+        if(vectors == undefined || vectors.length == 0) return new this;
+        let c = vectors.reduce( (sum, v) => { 
+            return this.add(sum, v);
+        }, new this);
+        return c.scalarMultiply(1.0 / vectors.length);
+    }
 }
 
 module.exports = Vec2;

lib/vec3.js

@@ -160,6 +160,13 @@ class Vec3 {
         return v1.squaredDistance(v2);
     }
 
+    static centroid(vectors) {
+        if(vectors == undefined || vectors.length == 0) return new this;
+        let c = vectors.reduce( (sum, v) => { 
+            return this.add(sum, v);
+        }, new this);
+        return c.scalarMultiply(1.0 / vectors.length);
+    }
 }
 
 module.exports = Vec3;