ylm_coef(l,m)  
  
     return sqrt((2*l+1)(l-m)!/(4*pi*(l+m)!)), the normalization  
     coefficient for spherical harmonic Ylm with respect to the  
     associated Legendre function Plm.  In this implementation,  
     0<=m<=l; use symmetry for m<0, or use sines and cosines  
     instead of complex exponentials.  Unlike Plm, array L and M  
     arguments are permissible here.  
     WARNING: These get combinitorially small with large L and M;  
     probably Plm is simultaneously blowing up and should be  
     normalized directly in legndr if what you want is Ylm.  But  
     I don't feel like working all that out -- if you need large  
     L and M results, you should probably be working with some  
     sort of asymptotic form anyway...  

unknown type function, documented at include/legndr.i   line 77