Usage: <tt>input = [ <i>ns  species_1 species_2 &hellip; species_ns</i> ]  fixatoms_by_species<tt>

<p>
If <tt><i>ns</i></tt> > 0, then all atoms <tt>i</tt> whose <tt>species[i]</tt> value matches any of 
the <tt><i>species_1 species_2 &hellip; species_ns</i> </tt> will have <tt>fixed[i] = 1</tt> set.

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