;+
; NAME:
;   oclc_fwd_h.pro
;
; PURPOSE:
;   Calculates the pressure scale height, h,
;
; DESCRIPTION:
;
; CALLING SEQUENCE:
;   h = oclc_fwd_h(r, t, mu, mp) 
;
; INPUTS: 
;   **** All inputs in cgs units ********
;
;   r - An array of radius values from the center of the planet, in cm.
;       The radius array could be in ascending or descending order.
;   t - An array (corresponding to r) or scalar of the temperature, 
;       in Kelvin.
;   mu - An array (corresponding to r) or scalar of the molecular weight
;         (unitless).
;   mp - the planetary mass, in grams.
;
; OUTPUTS:
;   h - pressure scale height in cm
;
; EXAMPLE 1 - scalar temperature, molecular weight
;   r = dindgen(200)*1d5 + 1200d5  ; array of r, in cm
;   r0 = 1250d5 ; reference r in cm
;   t = 104.d  ; scalar temperature in K
;   mu = 28.01d ; scalar molecular weight
;   mp = 1.3d25 ; reference planet mass in g
;   h = oclc_fwd_h(r, t, mu, mp)

;   ; ---- exact calculation, see Elliot and Young 1992
;   lam  =  (!phys.g*mp*mu*!phys.m_u/(!phys.k*t*r )) ;energy ratio
;   h2 = r/lam
;   
;   plot, r/1e5, (h-h2)/h2
;   print, minmax( (h-h2)/h2 )  ;
;   print, mean( (h-h2)/h2 )    ;
;
;
; EXAMPLE 2 - variable temperature
;   r = dindgen(200)*1d5 + 1200d5  ; array of r, in cm
;   r0 = 1250d5 ; reference r in cm
;   b = -2.d
;   t0 = 104.d 
;   t = t0 * (r/r0)^b  ; scalar temperature in K
;   mu = 28.01d ; scalar molecular weight
;   mp = 1.3d25 ; reference planet mass in g
;   h = oclc_fwd_h(r, t, mu, mp)

;   ; ---- exact calculation, see Elliot and Young 1992
;   lam  =  (!phys.g*mp*mu*!phys.m_u/(!phys.k*t *r )) ;energy ratio
;   h2 = r/lam
;   
;   plot, r/1e5, (h-h2)/h2
;   print, minmax( (h-h2)/h2 )  ;
;   print, mean( (h-h2)/h2 )    ;
;
; REVISON HISTORY:
; 25-Aug-2006 CBO SwRI -- modified from LAY's lightcurve.pro
; 23-Sep-2006 LAY SwRI -- changed some variable names, added example
; 
;- 
function oclc_fwd_h, r, t, mu, mp

    physconstants

    gravacc = !phys.g * mp / (r^2)
    sclhgt= !phys.k * t/(mu * !phys.m_u * gravacc)
    
    return, sclhgt
end