SUBROUTINE CORREL(DATA1,DATA2,N,ANS)
      PARAMETER(NMAX=8192)
      DIMENSION DATA1(N),DATA2(N)
      COMPLEX FFT(NMAX),ANS(N)
      CALL TWOFFT(DATA1,DATA2,FFT,ANS,N)
      NO2=FLOAT(N)/2.0
      DO 11 I=1,N/2+1
        ANS(I)=FFT(I)*CONJG(ANS(I))/NO2
11    CONTINUE
      ANS(1)=CMPLX(REAL(ANS(1)),REAL(ANS(N/2+1)))
      CALL REALFT(ANS,N/2,-1)
      RETURN
      END