二维程序如下：
      SUBROUTINE fourn(data,nn,ndim,isign)
    implicit double precision(a-h,o-z)
    dimension data(*),nn(ndim)
      ntot=1
      do 11 idim=1,ndim
        ntot=ntot*nn(idim)
11    continue
      nprev=1
      do 18 idim=1,ndim
        n=nn(idim)
        nrem=ntot/(n*nprev)
        ip1=2*nprev
        ip2=ip1*n
        ip3=ip2*nrem
        i2rev=1
        do 14 i2=1,ip2,ip1
          if(i2.lt.i2rev)then
            do 13 i1=i2,i2+ip1-2,2
              do 12 i3=i1,ip3,ip2
                i3rev=i2rev+i3-i2
                tempr=data(i3)
                tempi=data(i3+1)
                data(i3)=data(i3rev)
                data(i3+1)=data(i3rev+1)
                data(i3rev)=tempr
                data(i3rev+1)=tempi
12            continue
13          continue
          endif
          ibit=ip2/2
1         if ((ibit.ge.ip1).and.(i2rev.gt.ibit)) then
            i2rev=i2rev-ibit
            ibit=ibit/2
          goto 1
          endif
          i2rev=i2rev+ibit
14      continue
        ifp1=ip1
2       if(ifp1.lt.ip2)then
          ifp2=2*ifp1
          theta=isign*6.28318530717959d0/(ifp2/ip1)
          wpr=-2.d0*sin(0.5d0*theta)**2
          wpi=sin(theta)
          wr=1.d0
          wi=0.d0
          do 17 i3=1,ifp1,ip1
            do 16 i1=i3,i3+ip1-2,2
              do 15 i2=i1,ip3,ifp2
                k1=i2
                k2=k1+ifp1
                tempr=sngl(wr)*data(k2)-sngl(wi)*data(k2+1)
                tempi=sngl(wr)*data(k2+1)+sngl(wi)*data(k2)
                data(k2)=data(k1)-tempr
                data(k2+1)=data(k1+1)-tempi
                data(k1)=data(k1)+tempr
                data(k1+1)=data(k1+1)+tempi
15            continue
16          continue
            wtemp=wr
            wr=wr*wpr-wi*wpi+wr
            wi=wi*wpr+wtemp*wpi+wi
17        continue
          ifp1=ifp2
        goto 2
        endif
        nprev=n*nprev
18    continue
      return
      END

——————————————————————————————
    program abs
    implicit double precision(a-h,o-z)
    parameter(ndim=2,isign=1,nn=8)    
    dimension  data(2*nn*nn) ,grid(nn,nn),mm(2)
    mm(1)=8
    mm(2)=8
    do j=1,nn
    do i=1,nn
      grid(i,j)=2.5d0*sin(0.25d0*dble(i)+6.1d0*dble(j));  
    data(2*(j-1)*nn+2*i-1)=grid(i,j)
    data(2*(j-1)*nn+2*i)=0.d0
    enddo
    enddo
    call   fourn(data,mm,ndim,isign)
    write(*,'(f9.5))') (data(2*j-1)  ,j=1,nn*nn)  ！实数部分
    stop
    end
所得结果与matlab的结果不一样，是怎么个事情