;+
;FUNCTION mirrorang
;USAGE:
;  y = mirrorang(x,par=p)
;-

function mirrorang, e, parameters=p  $
   , p_names = p_names, pder_values= pder_values 

if not keyword_set(p) then $
   p = {brat:-6.d, e0:100.0d,  vdht:0.d }

a = sqrt(abs(1/p.brat)*(1+p.e0/e))
bad = where(a gt 1.,count)
if count ne 0 then a(bad) = !values.f_nan
a = asin(a)
if p.brat lt 0. then a= !pi - a
; ignore the following
;if keyword_set(p_names) then begin
;   np = n_elements(p_names)
;   nd = n_elements(f)
;   for i=0,np-1 do begin
;      case strlowcase(p_names(i)) of
;          'h': pder_values(*,i) = e
;          'l': pder_values(*,i) = p.h * e * x / p.l^2
;          'a0': pder_values(*,i) = 1
;          else: print,'Unknown Variable ', p_names(i)
;      endcase
;   endfor
;endif
print,'Do not use this routine'


return,a/!dtor
end