;+
; NAME:
;              ULY_CHIMAP_INIT
; PURPOSE:
;              Initialize the chi square map structure
;
; USAGE:
;              map = uly_chimap_init(<n_xnode>, <n_ynode>)
;
; ARGUMENTS:
;       X_NODE, Y_NODE
;              The number of x and y nodes of the chi square map structure.
;
; RETURN VALUE:
;              Initialized chi square map structure. Which contains:
;       .map    2d array with the computed chi2 values over xnode/ynode
;       .xnode  nodes on the abscissa where the chi2 is computed 
;       .ynode  nodes on the ordinate where the chi2 is computed 
;       .xtitle name of the x variable (for example age, tempreture...)
;       .ytitle name of the y variable (for example velocity, Fe/H...)
;       .xunit  units of the x variable (for example Myr, C...)
;       .yunit  units of the y variable (for example km/s, dex...)
;
; AUTHOR:
;              Antoine Bouchard
; HISTORY:
;              2008/02/08
;-
; CATEGORY:    ULY
;------------------------------------------------------------------------------
function uly_chimap_init, n_xnode, n_ynode
return, {map:fltarr(n_xnode,n_ynode)*!VALUES.F_NAN,     $
         xnode:fltarr(n_xnode)*!VALUES.F_NAN,           $
         ynode:fltarr(n_ynode)*!VALUES.F_NAN,           $
         xtitle:'',                                     $
         ytitle:'',                                     $
         xunit:'',                                      $
         yunit:''}
end