;------------------------------------------------------------
;------------------------------------------------------------
;------------------------------------------------------------
;+
; @file_comments 
; Send back a vector or a matrix constituted of 0 and 1 in alternation
;
; @categories 
; Function, Matrix
;
; @param n1 {in}{required} number of elements in the first dimension
; @param n2 {in}{required} number of elements in the second dimension
;
; @returns result
; 
; @history Sebastien Masson (smasson\@lodyc.jussieu.fr)
;                       1/12/98
;
; @version $Id$
;
;-
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;------------------------------------------------------------
;------------------------------------------------------------
function zero_one, n1,n2
;
  compile_opt idl2, strictarrsubs
;
   CASE N_PARAMS() OF
      1:return, findgen(n1) mod 2
      2:BEGIN 
         if fix(n1/2) EQ n1/2. then BEGIN ;even number of columns
            res = findgen(n1+1,n2) mod 2
            return, res[0:n1-1, *]
         ENDIF ELSE return, findgen(n1,n2) mod 2 ;odd number of columns
      END
      else: return,  report('bad number of arguments')
   endcase            
end