function dot( x, y ) {
	var len = x.length;
	var ret = 0;
	var i;

	for ( i = 0; i < len; i++ ) {
		ret += x[ i ] * y[ i ];
	}
	return ret;
}
Calculates the dot product of two vectors.

@private
@param {NumericArray} x - first vector
@param {NumericArray} y - second vector
@returns {number} dot product

@example
var x = [ 1.0, 2.0, 3.0 ];
var y = [ 1.0, 2.0, 2.0 ];

var ret = dot( x, y );
// returns 11.0