ype = single atom type 
    <LI>
    region = geometric region of atoms 
    <LI>
    bondtype = bondtype (only for assigning to fix style SHAKE) 
    <LI>
    angletype = angletype (only for assigning to fix style SHAKE) 
    <LI>
    remainder = rest of unconstrained atoms 
</UL>
<PRE>
coeffs:  atom
               (1) global atom #
         molecule
               (1) molecule #
         type
               (1) atom type
         region
               (1) lower x bound of region
               (2) upper x