NAME: 
   salb
 PURPOSE: 
   Compute single particle scattering albedo.
 DESCRIPTION:
 CATEGORY:
   Mathematical
 CALLING SEQUENCE:
   salb,radius,abscoef,se,si,w
 INPUTS:
   radius - Radius of particle, same units as 1/abscoef
   abscoef - absorption coefficient of material, units 1/radius
   se      - external scattering efficiency
   si      - internal scattering efficiency
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
 OUTPUTS:
   w       - single scattering albedo
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  Written by Marc W. Buie, Lowell Observatory, 1995 May 13