n    = 10
  evlr = random_uniform(-1,1,n)                  ; place-holder numbers

  evlr@eigright = random_uniform(10,20,(/n,n/))  ; place-holder numbers
  evlr@eigleft  = random_uniform(15,25,(/n,n/))
                                                 ; ncl-talk numbers
  evlr@eigr     = (/  0.8869482, 0.8869482, 0.9359075, 0.6810071, 0.6810071 \
                   ,-0.06872535, 0.0454572, 0.0454572, 0.192471 , 0.6176199 /) 
  evlr@eigi     = (/  0.1857084,-0.1857084,         0, 0.2888337, -0.2888337\
                   ,          0, 0.1147234,-0.1147234,         0,  0        /)
  evlr@eigv_length = (/  0.9061815, 0.9061815, 0.9359075, 0.7397267, 0.7397267 \
                      , 0.06872535, 0.123401 , 0.123401 , 0.192471 , 0.6176199/)

  printVarSummary(evlr)
  print("===")

;===
; ncl-talk:
; is that possible to sort the array by one of the attribute? 
; For example, I want the variable evlr show in descending order of the attribute eigv_length.
;===
; http://www.ncl.ucar.edu/Document/Functions/Built-in/dim_pqsort.shtml
; http://www.ncl.ucar.edu/Document/Functions/Built-in/dim_pqsort_n.shtml
;===

  kflag = -1 ; return the permutation vector resulting from sorting x in decreasing order and do not sort x. 
  
  id  = dim_pqsort(evlr@eigv_length, kflag)
  print(id)
  print("===")

  eigv_len_sort = evlr@eigv_length(id)
  eigr_sort     = evlr@eigr(id) 
  eigi_sort     = evlr@eigi(id) 

;http://www.ncl.ucar.edu/Document/Functions/Built-in/sprintf.shtml

  print(id+"  "+sprintf("%9.6f",eigv_len_sort)+" "+sprintf("%9.6f",eigr_sort)+" "+sprintf("%9.6f",eigi_sort))
  
  print("===")