function subtract( x, arr ) {
	var len;
	var res;
	var i;

	len = arr.length;
	res = new Array( len );
	for ( i = 0; i < len; i++ ) {
		res[ i ] = x - arr[ i ];
	}

	return res;
}
Computes an element-wise subtraction.

@private
@param {number} x - scalar minuend (implicitly broadcasted to full length array)
@param {NumericArray} arr - array of subtrahends
@returns {NumericArray} output array

@example
var x = 3;
var arr = [ 1, 2, 2, 3 ];

var y = subtract( x, arr );
// returns [ 2, 1, 1, 0 ]