function mean( arr ) {
	var delta;
	var len;
	var mu;
	var i;

	mu = 0.0;
	len = arr.length;
	for ( i = 0; i < len; i++ ) {
		delta = arr[ i ] - mu;
		mu += delta / (i+1);
	}
	return mu;
}
Computes the arithmetic mean of a numeric array.

@private
@param {NumericArray} arr - input array
@returns {number} arithmetic mean