;+
;
; From a time serie of length T=tinc*N
; Return power spectrum and array of periods
;
; @version
; $Id$
;
;-
FUNCTION spectrum, ts, tinc
;
  compile_opt idl2, strictarrsubs
;
  N=n_elements(ts)
  N21 = N/2
  ps=ABS(FFT(ts, -1))
  ps=ps[0:N21-1]

  period=tinc*N/(findgen(N21)+0.0000000000001)
  period[0]=99999999999.

  ret=findgen(2,N21)
  ret[1,*]=ps
  ret[0,*]=period

  return, ret
end