For every atom <tt>k</tt>, update its real coordinates from its scaled coordinates.

<p>
 <b>r</b><sub>k</sub> = <b>H</b> &sdot; <b>s</b><sub>k</sub>.

<p>
Usually we don't need to call this command, because always computes the real coordinates 
from the scaled coordinate inside the potential function.

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


