PROGRAM Ableitungen

IMPLICIT NONE

!_______________________________________________________________________________

#include'fftw3.f'

!_______________________________________________________________________________

INTEGER k
PARAMETER N=2048
DOUBLE PRECISION:: pi,kvec
DOUBLE COMPLEX:: imi
DIMENSION kvec(N/2+1)
INTEGER*8 plan_hin,plan_her
DOUBLE PRECISION:: in
DIMENSION in(N)
DOUBLE COMPLEX:: out
DIMENSION out(N/2 + 1)
!_______________________________________________________________________________
imi=(0.0d0,1.0d0)
pi=DACOS(-1.0d0)
!_______________________________________________________________________________
!Initialisierung des Feldes
open(10,File='Funktion.dat')
	DO k=1,N
	in(k)=dsin(2.0*pi*(k-1)/real(N))
	write(10,*) k-1,real(in(k))
	END DO
close(10)
!_______________________________________________________________________________
! Wellenzahlen initialisieren
	DO k=1,N/2+1
	kvec(k)=k-1
	END DO
!_______________________________________________________________________________
! Plaene initialisieren
 CALL dfftw_plan_dft_r2c_1d(plan_hin,N,in,out,FFTW_ESTIMATE)
 CALL dfftw_plan_dft_c2r_1d(plan_her,N,out,in,FFTW_ESTIMATE)
!_______________________________________________________________________________
! in den Fourierraum
CALL dfftw_execute_dft_r2c(plan_hin, in, out)
out=out/DBLE(N)**0.5d0
!_______________________________________________________________________________
! Ableitung berechnen
	DO k=1,N/2+1
	out(k)=imi*kvec(k)*out(k)
	END DO
open(13,File='AbleitungFourierraum.dat')
	DO k=1,N/2+1
	write(13,*) k-1,real(out(k))
	END DO
close(13)
!_______________________________________________________________________________
! in den Ortsraum
CALL dfftw_execute_dft_c2r(plan_her,out,in)
in=in/DBLE(N)**0.5d0
open(14,File='Ableitung.dat')
	DO k=1,N
	write(14,*) k-1,real(in(k))
	END DO
close(14)
!_______________________________________________________________________________
!Zerstörung der Plaene
CALL dfftw_destroy_plan(plan_hin)
CALL dfftw_destroy_plan(plan_her)
!_______________________________________________________________________________
END PROGRAM