function gcusum( N, sum, x, strideX, y, strideY ) {
	var ox = stride2offset( N, strideX );
	var oy = stride2offset( N, strideY );
	return ndarray( N, sum, x, strideX, ox, y, strideY, oy );
}
Computes the cumulative sum of strided array elements.

@param {PositiveInteger} N - number of indexed elements
@param {number} sum - initial sum
@param {NumericArray} x - input array
@param {integer} strideX - stride length for `x`
@param {NumericArray} y - output array
@param {integer} strideY - stride length for `y`
@returns {NumericArray} output array

@example
var x = [ 1.0, -2.0, 2.0 ];
var y = [ 0.0, 0.0, 0.0 ];

var v = gcusum( x.length, 0.0, x, 1, y, 1 );
// returns [ 1.0, -1.0, 1.0 ]