;+
;
; @file_comments
; We want, from a 3d matrix, to extract a 2d (x,y) array whose each element
; has been extract from a level specified by the 2d level array (typically,
; we want to obtain the salinity along an isopycn we have repered by its level).
; level2index is a function who give, in function of level, a 2d indexes array
; which will allow to extract the 2d array from the 3d array...
;
; @categories
; Without loop
;
; @param LEVEL {in}{required}{type=2d array}
; A 2d level array
;
; @returns
; a 2d indexes array
;
; @history
; Sebastien Masson (smasson\@lodyc.jussieu.fr)
;                      24/11/1999
;
; @version
; $Id$
;
;-
;
FUNCTION level2index, level
; An element of 3d array (whose the two first dimensions are nx and ny) whose
; coordinates are i, j and k have for index in the same 3d array i + j*nx + k*(nx*ny)
; level given, for  each point of level, we know i, j et k,
; so we can calculate the index
;
  compile_opt idl2, strictarrsubs
;
   taille = size(level)
   nx = taille[1]
   ny = taille[2]
; array k*(nx*ny)
   tabknxny = (nx*ny)*long(level)
;
;
   return, lindgen(nx, ny)+tabknxny
end