NAME:
	bidr
 PURPOSE: (one line)
	Compute the bi-directional reflectance (old Hapke formula).
 DESCRIPTION:
 CATEGORY:
  Miscellaneous
 CALLING SEQUENCE:
	ans = bidr(w,emu,smu,g,holes,pzero)
 INPUTS:
	w     - Single scattering albedo.
	emu   - Cosine of the emission angle.
	smu   - Cosine of the incidence angle.
  g     - Phase angle, in radians.
	holes - Compaction parameter value (1981 formalism).
	pzero - Value of the single particle phase function.
 OPTIONAL INPUT PARAMETERS:
	None.
 KEYWORD PARAMETERS:
	None.
 OUTPUTS:
	Return value is the bi-directional reflectance.
 COMMON BLOCKS:
	None.
 SIDE EFFECTS:
	None.
 RESTRICTIONS:
       Any input may be a vector.  If more than one is a vector then the
       lengths must match.  The return will have the same dimensions as
       the input.
 PROCEDURE:
 MODIFICATION HISTORY:
       Written 1991 December, by Marc W. Buie, Lowell Observatory
       97/08/21, MWB, fixed phase angle bug, added g as input argument.