NAME:
   getsalb2
 PURPOSE: (one line)
   Solve for single scattering albedo given bi-directional reflectance
 DESCRIPTION:
 CATEGORY:
   Miscellaneous
 CALLING SEQUENCE:
   ans = getsalb2(bidref,emu,smu,g,holes,p,b0,theta)
 INPUTS:
   bidref - The bi-directional reflectance.
   emu    - Cosine of the emission angle.
   smu    - Cosine of the incidence angle.
   g      - Phase angle, in radians.
   holes  - Compaction parameter value (1981 formalism).
   p      - Value of the single particle phase function.
   theta  - Surface roughness value.  (radians)
 OPTIONAL INPUT PARAMETERS:
   None.
 KEYWORD PARAMETERS:
  H93   - Flag, if set, uses the 1993 version of Hapke's approximation to the
            Chandresekar H function.  The 1993 version is more accurate but
            considerably slower to compute.
 OUTPUTS:
   returns the single scattering albedo.
 COMMON BLOCKS:
   None.
 SIDE EFFECTS:
   None.
 RESTRICTIONS:
   This works on scalar input only.
 PROCEDURE:
 MODIFICATION HISTORY:
   Written 2003/10/23, by Marc W. Buie, Lowell Observatory, cloned
     from getsalb.pro
   2016/01/10, MWB, changed tolerance from 0.005 to 0.001 on salb