function gnrm2( N, x, stride ) {
	return ndarray( N, x, stride, stride2offset( N, stride ) );
}
Computes the L2-norm of a vector.

@param {PositiveInteger} N - number of indexed elements
@param {NumericArray} x - input array
@param {PositiveInteger} stride - stride length
@returns {number} L2-norm

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

var z = gnrm2( x.length, x, 1 );
// returns 3.0