function gapx( N, alpha, x, strideX ) {
	return ndarray( N, alpha, x, strideX, stride2offset( N, strideX ) );
}
Adds a scalar constant to each element in a strided array.

@param {PositiveInteger} N - number of indexed elements
@param {number} alpha - scalar constant
@param {NumericArray} x - input array
@param {integer} strideX - stride length
@returns {NumericArray} input array

@example
var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];

gapx( x.length, 5.0, x, 1 );
// x => [ 3.0, 6.0, 8.0, 0.0, 9.0, 5.0, 4.0, 2.0 ]