code: public static void center(Point3d[] x) {
  		Point3d center = centroid(x);
  		center.negate();
  		translate(new Vector3d(center), x);
  	}
docs: Center a cloud of points. This means subtracting the {@lin
  #centroid(Point3d[])} of the cloud to each point.
  
  @param x
  array of points. Point objects will be modified