C FFTC.FT FFT-V4A 4/22/76 SUBROUTINE FFTC (A,N,M,SGNEX) C-------FFT VON N=2**M KOMPLEXEN DATEN C A = IN- UND OUTPUTARRAY, LAENGE N=2**M, KOMPLEX C-------SGNEXP = VORZEICHEN DES EXPONENTEN DER E-FUNKTIONEN DIMENSION A(2,513) DIMENSION U(2),W(2),T(2),V(2) NV2=N/2 NM1=N-1 J=1 DO 7 I=1,NM1 IF (I.GE.J) GOTO 5 T(1)=A(1,J) T(2)=A(2,J) A(1,J)=A(1,I) A(2,J)=A(2,I) A(1,I)=T(1) A(2,I)=T(2) 5 K=NV2 6 IF (K.GE.J) GOTO 7 J=J-K K=K/2 GO TO 6 7 J=J+K PI=3.141592653*SGNEX LE1=1 S=0. DO 30 L=1,M LE=2*LE1 U(1)=1. U(2)=0. SN=SIN(PI/FLOAT(LE)) W(1)=-2.*SN*SN W(2)=S S=SN DO 20 J=1,LE1 DO 10 I=J,N,LE IP=I+LE1 T(1)=A(1,IP)*U(1)-A(2,IP)*U(2) T(2)=A(1,IP)*U(2)+A(2,IP)*U(1) A(1,IP)=A(1,I)-T(1) A(2,IP)=A(2,I)-T(2) A(1,I)=A(1,I)+T(1) A(2,I)=A(2,I)+T(2) 10 CONTINUE V(1)=U(1)+U(1)*W(1)-U(2)*W(2) V(2)=U(2)+U(1)*W(2)+U(2)*W(1) U(1)=V(1) U(2)=V(2) COR=.5-.5*(U(1)*U(1)+U(2)*U(2)) U(1)=COR*U(1)+U(1) 20 U(2)=COR*U(2)+U(2) 30 LE1=LE RETURN END