subroutine indexx(n,arr,indx)

  parameter (NMAX=3000)
  integer indx(n)
  real arr(n)
  real brr(NMAX)
  if(n.gt.NMAX) then
     print*,'n=',n,' too big in indexx.'
     stop
  endif
  do i=1,n
     brr(i)=arr(i)
     indx(i)=i
  enddo
  call ssort(brr,indx,n,2)

  return
end subroutine indexx