Sader, John E.
Hughes, Barry D.
Huber, Ferdinand
Giessibl, Franz J.
Article History
First Online: 6 December 2018
Change Date: 9 January 2019
Change Type: Correction
Change Details: In the version of this Comment originally published, equation (4) was incorrect; see the correction notice for details. This has now been corrected in the online versions of the Comment.
Competing interests
: The authors declare no competing interests.