If <tt>conj_fixbox = 1</tt> then in the conjugate gradient relaxation
(invoked by the <tt>relax</tt> command), the box matrix <b>H</b> is not
allowed to change.  

<p>
If <tt>conj_fixbox = 0</tt> then the box matrix <b>H</b> is allowed to change
during relaxation.

<p>
Also see <tt>conj_fixboxvec</tt>.

