allocate_arrays Subroutine

  subroutine allocate_arrays
    use kt_grids, only: ntheta0, naky, is_box
    use array_utils, only: zero_array
    use theta_grid, only: ntgrid, shat
    use dist_fn_arrays, only: g, gnew, g_work
    use dist_fn_arrays, only: kx_shift, theta0_shift   ! MR
    use dist_fn_arrays, only: gexp_1, gexp_2, gexp_3
    use dist_fn_arrays, only: antot, antota, antotp
    use dist_fn_arrays, only: fieldeq, fieldeqa, fieldeqp
    use gs2_layouts, only: g_lo
    use nonlinear_terms, only: nonlin, split_nonlinear
    use run_parameters, only: has_apar
    use array_utils, only: zero_array
    use warning_helpers, only: is_zero
#ifdef SHMEM
    use shm_mpi3, only : shm_alloc
#endif
    implicit none

    if (.not. allocated(g)) then
       allocate (g      (-ntgrid:ntgrid,2,g_lo%llim_proc:g_lo%ulim_alloc))
       allocate (gnew   (-ntgrid:ntgrid,2,g_lo%llim_proc:g_lo%ulim_alloc))
       allocate (g_work (-ntgrid:ntgrid,2,g_lo%llim_proc:g_lo%ulim_alloc))
       allocate (g_h  (-ntgrid:ntgrid,2,g_lo%llim_proc:g_lo%ulim_alloc))
       call zero_array(g) ; call zero_array(gnew) ; call zero_array(g_work)
       call zero_array(g_h)

       if(opt_source)then
          allocate (source_coeffs_phim(-ntgrid:ntgrid-1,2,g_lo%llim_proc:g_lo%ulim_alloc))
          allocate (source_coeffs_phip(-ntgrid:ntgrid-1,2,g_lo%llim_proc:g_lo%ulim_alloc))
          if(has_apar)then
             allocate (source_coeffs_aparm(-ntgrid:ntgrid-1,2,g_lo%llim_proc:g_lo%ulim_alloc))
             allocate (source_coeffs_aparp(-ntgrid:ntgrid-1,2,g_lo%llim_proc:g_lo%ulim_alloc))
          endif
       endif

       if (nonlin .and. .not. split_nonlinear) then
#ifndef SHMEM
          allocate (gexp_1(-ntgrid:ntgrid,2,g_lo%llim_proc:g_lo%ulim_alloc))
#else
          call shm_alloc(gexp_1, [-ntgrid, ntgrid, 1, 2, g_lo%llim_proc, g_lo%ulim_alloc])
#endif
          allocate (gexp_2(-ntgrid:ntgrid,2,g_lo%llim_proc:g_lo%ulim_alloc))
          allocate (gexp_3(-ntgrid:ntgrid,2,g_lo%llim_proc:g_lo%ulim_alloc))
          call zero_array(gexp_1) ; call zero_array(gexp_2) ; call zero_array(gexp_3)
       end if

       if (abs(g_exb*g_exbfac) > epsilon(0.)) then           ! MR
          if (is_box .or. is_zero(shat)) then
             allocate (kx_shift(naky))
             kx_shift = 0.
          else
             allocate (theta0_shift(naky))
             theta0_shift = 0.
          endif
       endif                           ! MR end
    endif

    allocate (antot (-ntgrid:ntgrid,ntheta0,naky))
    allocate (antota(-ntgrid:ntgrid,ntheta0,naky))
    allocate (antotp(-ntgrid:ntgrid,ntheta0,naky))
    call zero_array(antot) ; call zero_array(antota) ; call zero_array(antotp)

    allocate (fieldeq (-ntgrid:ntgrid,ntheta0,naky))
    allocate (fieldeqa(-ntgrid:ntgrid,ntheta0,naky))
    allocate (fieldeqp(-ntgrid:ntgrid,ntheta0,naky))
    call zero_array(fieldeq) ; call zero_array(fieldeqa) ; call zero_array(fieldeqp)
  end subroutine allocate_arrays