correlation Subroutine

  subroutine correlation (cfnc_2pi)
    use kt_grids, only: naky, ntheta0
    use theta_grid, only: ntgrid
    use fields_arrays, only: phinew
    implicit none
    complex, dimension (-ntgrid:,:), intent (out) :: cfnc_2pi
    integer :: ik, it, ig
    real :: fac

    cfnc_2pi = 0.0

    do ik = 1, naky
       if (ik==1) then
          fac = 1.0
       else
          fac = 0.5
       end if
       do it = 1, ntheta0
          do ig = -ntgrid, ntgrid
             cfnc_2pi(ig,ik) = cfnc_2pi(ig,ik) + phinew(0,it,ik)*conjg(phinew(ig,it,ik))*fac
          end do
       end do
    end do

  end subroutine correlation