;+
; NAME:
;  n2t
; PURPOSE: (one line)
;  Return vapor pressure of N2 from Brown & Ziegler 1980
; CATEGORY:
;  Volatile Transport
; CALLING SEQUENCE:
;  t = n2t(vp)
; INPUTS:
;  vp : vapor pressure in microbar
; KEYWORD INPUTS
;  None
; OUTPUTS:
;  t : temperature, K
; OPTIONAL OUTPUT
;  None
; RESTRICTIONS:
; PROCEDURE:
;  This function implements the tables of Brown and Zeigler 
; MODIFICATION HISTORY:
;  Written 2013 Jun 16, by Leslie Young, SwRI
;-
function n2t, p

if isarray(p) then begin
   t = 0. * p
   for i = 0, n_elements(p)-1 do t[i] = n2t(p[i])
   return, t
endif

; Return N2 temperature as a function of vapor pressure in microbar
a_liq  =[1.51050147e1, -6.15496072e2, -2.31314834e3, -5.89850934e4, 0.]
a_beta= [1.64302619e1, -6.50497257e2, -8.52432256e3,  1.55914234e5, -1.06368300e6]
a_alpha=[1.88550118e1, -8.57102332e2, -1.01891053e3,  1.28466570e4, -4.82177497e4]
a=a_beta
if p lt n2vp(35.62) then a=a_alpha
if p gt n2vp(63.152) then a=a_gamma
a[0] = a[0] - alog(p/1.33322e3)
roots = fz_roots(a)
gd = where( imaginary(roots) eq 0 and real_part(roots) gt 0, ngd)
t = 1/real_part(roots[gd[0]])
return, t
end