The 3x3 matrix <b>H</b> consists of three column vectors
[<b>c</b><sub>1</sub> | <b>c</b><sub>2</sub> | <b>c</b><sub>3</sub> ], 
which are the repeat vector of the simulation cell (under periodic boundary
conditions).

<p>
See <a href="http://micro.stanford.edu/wiki/Output_File_Formats_in_MD++#Configuration_.cn_File">wiki
page</a> for more details.
