subroutine IDFT(nmax,mmax,gf,g)
      integer nmax, mmax
      real g(0:nmax)
      complex gf(-mmax/2:mmax/2), gb(0:nmax)
      complex W, i
      real pi

      pi=3.14159
      i=(0.0,1.0)
      W=exp(2.0*i*pi/(nmax+1))
      do 10 j=0,nmax
         gb(j)=gf(-mmax/2)
         do 20 k=-mmax/2+1,mmax/2
            gb(j)=gb(j)+gf(k)*(W**(j*k))
  20  continue
         g(j)=real(gb(j))
  10  continue
      return
      end