NAME:
  fn_hg2a

 PURPOSE:
  Evaluate the 2-parameter Henyey-Greenstein phase function (alternate).

 DESCRIPTION:
    different normilzation from fn_hg2

 CATEGORY:
  Mathematical

 CALLING SEQUENCE:
  FN_HG3, g, a, F, /radians

 INPUTS:
     g: Phase angle(s) in degrees.
     a: Array of parameters:
          A[0] = asymmetry (ought to be positive)
          A[1] = forward fraction (between 0 and 1)

 OPTIONAL INPUT PARAMETERS:

 KEYWORD INPUT PARAMETERS:
     radians:  Phase angle is in radians instead of default degrees.

 OUTPUTS:
     F: The value of the function at each g.

 KEYWORD OUTPUT PARAMETERS:

 OPTIONAL OUTPUT PARAMETERS:

 COMMON BLOCKS:
  None.

 SIDE EFFECTS:
  None.

 RESTRICTIONS:
  None.

 PROCEDURE:
 MODIFICATION HISTORY:
  2023/08/01 Created by Marc Buie (based on fn_HG2.pro)