subroutine gather_4

  ! Writing out the velocities and scalars in X-space
  ! to the real*4 file

  use m_parameters
  use m_fields
  use m_work
  use x_fftw
  use m_les
  use m_fdm_calc

  implicit none

  integer :: n_out, n, i, j, k
  real*8  :: wmag2, rkmax2

  ! every variable will undergo a mode truncation for all modes
  ! that are higher than kmax.  This will ensure that the written
  ! variables are isotropic

  rkmax2 = real(kmax,8)**2

  ! number of variables to write out
  n_out = 3

  ! putting all variables in wrk array
  do k = 1,nz
     do j = 1,ny
        do i = 1,nx+2
           wmag2 = akx(i)**2 + aky(k)**2 + akz(j)**2

           if (wmag2 .gt. rkmax2) then
              wrk(i,j,k,1:n_out) = zip
           else
              wrk(i,j,k,1:n_out) = fields(i,j,k,1:n_out)
           end if

        end do
     end do
  end do

  ! velocities
  call xFFT3d(-1,1)
  call xFFT3d(-1,2)
  call xFFT3d(-1,3)

  u_(1:nx,1:ny,1:nz) = wrk(1:nx,1:ny,1:nz,1)
  v_(1:nx,1:ny,1:nz) = wrk(1:nx,1:ny,1:nz,2)
  w_(1:nx,1:ny,1:nz) = wrk(1:nx,1:ny,1:nz,3)


  return
end subroutine gather_4