FUNCTION flux_to_lup, flux, flux_err, b_soft

; Description: This function is called by the module "plot_light_motion_curve.pro".
;
; Author: Dan Bramich (dan.bramich@hotmail.co.uk)
;
; Dependencies: None
;
; History:
;
;   21/05/2013 - Module created (dmb).


;Convert flux to luptitude
value = flux/(2.0D*b_soft)
lup = (-2.5D/alog(10.0D))*(asinh(value) + alog(b_soft))
lup_err = (1.25D/(b_soft*alog(10.0D)))*sqrt(1.0D/(1.0D + (value^2)))*flux_err

;Return the luptitude and its error
return, [lup, lup_err]

END