;+ ; NAME: ; fn_hg2 ; ; PURPOSE: ; Evaluate the 2-parameter Henyey-Greenstein phase function. ; ; DESCRIPTION: ; ; 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: ; 2001-Nov-19 Created by Will Grundy (based on fn_HG3.pro) ;- pro fn_hg2,g,a,F,radians=radians on_error,2 ; Return to caller if an error occurs fn_hg1,g,abs(a[0]),fwd,radians=radians fn_hg1,g,-abs(a[0]),bkwd,radians=radians F = a[1]*fwd + (1.0-a[1])*bkwd return end