FUNCTION intersection,a,b
;+
; general purpose routine to return the intersection
; (i.e. common elements) of two vectors. Uses USERLIB
; routine UNIQ to obtain unique elements of a,b
; Written by M.J.Dutch June-1994.
; Centre de Recherches en Physique des Plasmas, EPFL, Switzerland
;-

ab=[a(uniq(a,sort(a))),b(uniq(b,sort(b)))] ; combine unique elements of a,b
ab=ab(sort(ab))                            ; sort the combined vector
nab=n_elements(ab)
diff=ab(1:nab-1)-ab(0:nab-2)
ind=where(diff eq 0)                       ; find repeated elements
if (ind(0) ne -1) then return,ab(ind) else return,-999

end