functions in drat.i - u

    update_mesh, mesh, rt, zt  
 or update_mesh, mesh, rt, zt, ireg  


updates the opaque MESH object to reflect a new RT, ZT, and  
(optionally) IREG.  The boundary edges are recomputed and stored  
in MESH, as well.  
Builtin function, documented at i0/drat.i   line 1086