fourier1d.f90

Ground state of the time-independent Gross-Pitaevskii equation

!***
! The following code is for use with the DFFTPACK library
!***

module fft_data
  integer, parameter :: dp=kind(1.d0)
  real(dp) :: fact
  real(dp), dimension(:), allocatable :: wsave
end module fft_data


subroutine fft_init(ng)
  !
  ! Initialize the Fourier transform
  !
  use fft_data
  implicit none

  integer, intent(in) :: ng

  allocate(wsave(2*ng+15))

  call dffti(ng,wsave)

  fact = 1.d0/real(ng,dp)

  return
end subroutine fft_init


subroutine fourier1D(ng,fin,fout,direction)
  !
  ! 1D Fourier transform
  !
  use fft_data
  implicit none

  integer, intent(in) :: ng
  real(dp), dimension(ng), intent(in) :: fin
  real(dp), dimension(ng), intent(out) :: fout
  integer, intent(in) :: direction

  if(direction >= 0) then
     ! Forward transform
     fout = fin
     call dfftf(ng,fout,wsave)
  else
     ! Backward transform
     fout = fin
     call dfftb(ng,fout,wsave)
     fout = fout*fact
  end if

  return
end subroutine fourier1D