function accumulator( vec ) {
		var i;
		if ( arguments.length === 0 ) {
			return out;
		}
		for ( i = 0; i < ndims; i++ ) {
			acc[ i ]( vec.get( i ) );
		}
		return out;
	}
If provided a data point vector, updates the mean vector and associated standard deviation along each dimension. If not provided a data point vector, returns the current mean vector and associated standard deviation along each dimension.

@private
@param {ndarray} [vec] - data point vector
@returns {Float64Array} current mean vector and associated standard deviation along each dimension