subroutine hps(x,m,n,dx,hpfre,lpfre)
c
c apply a recursive Butterworth high pass filter (zero phase)
c             OR (if lpfre < 0.95*Nyquist_freq )
c apply a recursive Butterworth band pass filter (zero phase)
c
c derived from xapiir
c a.tento 4/02 v.1.0
c a.tento 4/03 v.2.0 (+ band pass)
c a.tento 10/03 v.2.1 (+ low pass)
c
       implicit none
       integer m, n, j
       real x, dx, hpfre, lpfre
       dimension x(m,3) 
c
       real fny
c
c
       fny = 0.95 / (2.0 * dx)
c
c if lpfre too high NO band pass --> only high pass
c
       if ( lpfre  .gt.  fny ) then
       call rmean(x,m,n)
       do 1 j = 1, 3
       call xhpf(x(1,j),n,hpfre,dx) 
1      continue
c
       else
c
       if ( hpfre  .gt.  fny ) then        
          do 3 j = 1, 3
             call xlpf(x(1,j),n,lpfre,dx) 
3         continue
        else
          call rmean(x,m,n)
          do 2 j = 1, 3
             call xbpf(x(1,j),n,hpfre,lpfre,dx) 
2         continue
       endif       
c
       endif       
c
c
       return
c
       end