pro anomaly, e, ma, ea, dea
;
; Given the orbital eccentricity  e  and mean anomaly  ma  (in radians)
; of an orbiting body, this procedure solves Kepler's equation for the
; eccentric anomaly  ea  (in radians).
;
; B. Knapp, 1998.12.14
;
; RCS Data
;
; $Header: /home/betelgeuse/knapp/idllib/RCS/anomaly.pro,v 1.1 1999/12/02 21:11:40 knapp Exp $
;
; $Log: anomaly.pro,v $
; Revision 1.1  1999/12/02 21:11:40  knapp
; Initial revision
;
; Initial estimate (from Lawrence G. Taff, Celestial Mechanics, 1985)
  m = ma mod (2.d0*!dpi)
  ea = m+e*sin(m)/(1.d0+sin(m)-sin(m+e))
;
; Newton-Raphson iteration
  kmax = 100
  k = 0
; print, k, ea*!radeg
  repeat begin
     dea = (ea-e*sin(ea)-m)/(1.0d0-e*cos(ea))
     ea = ea-dea
     k = k+1
;    print, k, ea*!radeg
  endrep until abs(dea) lt 1.0d-14 or k ge kmax
;
  return
  end