The Helmert sub-matrix is returned. It is an orthogonal matrix without the first row.
References
Tsagris M.T., Preston S. and Wood A.T.A. (2011). A data-based power transformation for compositional data.
In Proceedings of the 4th Compositional Data Analysis Workshop, Girona, Spain. http://arxiv.org/pdf/1106.1451.pdf
John Aitchison (2003). The Statistical Analysis of Compositional Data p. 99 Blackburn Press.
Lancaster H. O. (1965). The Helmert matrices. The American Mathematical Monthly 72(1): 4-12.