function variance( N, correction, x, stride ) {
	return variancepn( N, correction, x, stride );
}
Computes the variance of a strided array.

@param {PositiveInteger} N - number of indexed elements
@param {number} correction - degrees of freedom adjustment
@param {NumericArray} x - input array
@param {integer} stride - stride length
@returns {number} variance

@example
var x = [ 1.0, -2.0, 2.0 ];
var N = x.length;

var v = variance( N, 1, x, 1 );
// returns ~4.3333