shiftedPBCs Subroutine

  subroutine shiftedPBCs
      ! Nudge the flow in a region near the outlet
      use modglobal, only : ib, itot, ie, jb, je, kb, ke, xh, ds, dyi, xlen, rk3step, dt, pi
      use modfields, only : u0, v0, w0, u0av, up, vp, wp
      use decomp_2d, only : zstart

      integer :: i, j, k, ig, il
      real :: vs, rk3coef
      real, dimension(ib:ie) :: sinfac

      if (ds > 0) then
      rk3coef = dt / (4. - real(rk3step))
      ! ig > itot/2 selects a contiguous local range il..ie; precompute the
      ! i-dependent sine once per column and run i innermost (see #330)
      il = max(ib, int(itot/2) - zstart(1) + 2)
      do i = il,ie
         ig = i + zstart(1) - 1 ! global i position
         sinfac(i) = sin(pi*(xh(ig)-xh(int(itot/2))) / (0.5*xlen))
      end do
      do k = kb,ke
         do j = jb,je
            do i = il,ie
               vs = 0.5 * pi * ds / (0.5*xlen) * u0av(k) * sinfac(i)
               up(i,j,k) = up(i,j,k) - vs * (u0(i,j,k) - u0(i,j-1,k)) * dyi
               vp(i,j,k) = vp(i,j,k) - vs * (v0(i,j,k) - v0(i,j-1,k)) * dyi
               wp(i,j,k) = wp(i,j,k) - vs * (w0(i,j,k) - w0(i,j-1,k)) * dyi
            end do
         end do
      end do

      end if

   end subroutine shiftedPBCs