FUNCTION percentile,x,p

; Returns the pth percentile of the array x, which
; is assumed to be sorted in increasing order.

; B. G. Knapp, 1986-12-11
;              1998-06-09, IDL v. 5 compliance
;              2000-05-01, Change FIX(r) to LONG(r)

  n = N_ELEMENTS(x)-1
  r = n*p*.01
  m = LONG(r)
  f = r MOD 1.
  RETURN,(1-f)*x[m]+f*x[(m+1)<n]

END