SUBROUTINE FAX(IFAX,N,MODE) SAVE DIMENSION IFAX(10) C NN=N IF (IABS(MODE).EQ.1) GO TO 10 IF (IABS(MODE).EQ.8) GO TO 10 NN=N/2 IF ((NN+NN).EQ.N) GO TO 10 IFAX(1)=-99 RETURN 10 K=1 C TEST FOR FACTORS OF 4 20 IF (MOD(NN,4).NE.0) GO TO 30 K=K+1 IFAX(K)=4 NN=NN/4 IF (NN.EQ.1) GO TO 80 GO TO 20 C TEST FOR EXTRA FACTOR OF 2 30 IF (MOD(NN,2).NE.0) GO TO 40 K=K+1 IFAX(K)=2 NN=NN/2 IF (NN.EQ.1) GO TO 80 C TEST FOR FACTORS OF 3 40 IF (MOD(NN,3).NE.0) GO TO 50 K=K+1 IFAX(K)=3 NN=NN/3 IF (NN.EQ.1) GO TO 80 GO TO 40 C NOW FIND REMAINING FACTORS 50 L=5 INC=2 C INC ALTERNATELY TAKES ON VALUES 2 AND 4 60 IF (MOD(NN,L).NE.0) GO TO 70 K=K+1 IFAX(K)=L NN=NN/L IF (NN.EQ.1) GO TO 80 GO TO 60 70 L=L+INC INC=6-INC GO TO 60 80 IFAX(1)=K-1 C IFAX(1) CONTAINS NUMBER OF FACTORS C IFAX(1) CONTAINS NUMBER OF FACTORS NFAX=IFAX(1) C SORT FACTORS INTO ASCENDING ORDER IF (NFAX.EQ.1) GO TO 110 DO 100 II=2,NFAX ISTOP=NFAX+2-II DO 90 I=2,ISTOP IF (IFAX(I+1).GE.IFAX(I)) GO TO 90 ITEM=IFAX(I) IFAX(I)=IFAX(I+1) IFAX(I+1)=ITEM 90 CONTINUE 100 CONTINUE 110 CONTINUE RETURN END SUBROUTINE FFTRIG(TRIGS,N,MODE) SAVE DIMENSION TRIGS(1) C PI=2.0*ASIN(1.0) IMODE=IABS(MODE) NN=N IF (IMODE.GT.1.AND.IMODE.LT.6) NN=N/2 DEL=(PI+PI)/FLOAT(NN) L=NN+NN DO 10 I=1,L,2 ANGLE=0.5*FLOAT(I-1)*DEL TRIGS(I)=COS(ANGLE) TRIGS(I+1)=SIN(ANGLE) 10 CONTINUE IF (IMODE.EQ.1) RETURN IF (IMODE.EQ.8) RETURN DEL=0.5*DEL NH=(NN+1)/2 L=NH+NH LA=NN+NN DO 20 I=1,L,2 ANGLE=0.5*FLOAT(I-1)*DEL TRIGS(LA+I)=COS(ANGLE) TRIGS(LA+I+1)=SIN(ANGLE) 20 CONTINUE IF (IMODE.LE.3) RETURN DEL=0.5*DEL LA=LA+NN IF (MODE.EQ.5) GO TO 40 DO 30 I=2,NN ANGLE=FLOAT(I-1)*DEL TRIGS(LA+I)=2.0*SIN(ANGLE) 30 CONTINUE RETURN 40 CONTINUE DEL=0.5*DEL DO 50 I=2,N ANGLE=FLOAT(I-1)*DEL TRIGS(LA+I)=SIN(ANGLE) 50 CONTINUE RETURN END SUBROUTINE VPASSM(A,B,C,D,TRIGS,INC1,INC2,INC3,INC4,LOT,N,IFAC,LA) SAVE DIMENSION A(N),B(N),C(N),D(N),TRIGS(N) DATA SIN36/0.587785252292473/,COS36/0.809016994374947/, * SIN72/0.951056516295154/,COS72/0.309016994374947/, * SIN60/0.866025403784437/ C M=N/IFAC IINK=M*INC1 JINK=LA*INC2 JUMP=(IFAC-1)*JINK IBASE=0 JBASE=0 IGO=IFAC-1 IF (IGO.GT.4) RETURN GO TO (10,50,90,130),IGO C C CODING FOR FACTOR 2 C 10 IA=1 JA=1 IB=IA+IINK JB=JA+JINK DO 20 L=1,LA I=IBASE J=JBASE DO 15 IJK=1,LOT C(JA+J)=A(IA+I)+A(IB+I) D(JA+J)=B(IA+I)+B(IB+I) C(JB+J)=A(IA+I)-A(IB+I) D(JB+J)=B(IA+I)-B(IB+I) I=I+INC3 J=J+INC4 15 CONTINUE IBASE=IBASE+INC1 JBASE=JBASE+INC2 20 CONTINUE IF (LA.EQ.M) RETURN LA1=LA+1 JBASE=JBASE+JUMP DO 40 K=LA1,M,LA KB=K+K-2 C1=TRIGS(KB+1) S1=TRIGS(KB+2) DO 30 L=1,LA I=IBASE J=JBASE DO 25 IJK=1,LOT C(JA+J)=A(IA+I)+A(IB+I) D(JA+J)=B(IA+I)+B(IB+I) C(JB+J)=C1*(A(IA+I)-A(IB+I))-S1*(B(IA+I)-B(IB+I)) D(JB+J)=S1*(A(IA+I)-A(IB+I))+C1*(B(IA+I)-B(IB+I)) I=I+INC3 J=J+INC4 25 CONTINUE IBASE=IBASE+INC1 JBASE=JBASE+INC2 30 CONTINUE JBASE=JBASE+JUMP 40 CONTINUE RETURN C C CODING FOR FACTOR 3 C 50 IA=1 JA=1 IB=IA+IINK JB=JA+JINK IC=IB+IINK JC=JB+JINK DO 60 L=1,LA I=IBASE J=JBASE DO 55 IJK=1,LOT C(JA+J)=A(IA+I)+(A(IB+I)+A(IC+I)) D(JA+J)=B(IA+I)+(B(IB+I)+B(IC+I)) C(JB+J)=(A(IA+I)-0.5*(A(IB+I)+A(IC+I))) X -(SIN60*(B(IB+I)-B(IC+I))) C(JC+J)=(A(IA+I)-0.5*(A(IB+I)+A(IC+I))) X +(SIN60*(B(IB+I)-B(IC+I))) D(JB+J)=(B(IA+I)-0.5*(B(IB+I)+B(IC+I))) X +(SIN60*(A(IB+I)-A(IC+I))) D(JC+J)=(B(IA+I)-0.5*(B(IB+I)+B(IC+I))) X -(SIN60*(A(IB+I)-A(IC+I))) I=I+INC3 J=J+INC4 55 CONTINUE IBASE=IBASE+INC1 JBASE=JBASE+INC2 60 CONTINUE IF (LA.EQ.M) RETURN LA1=LA+1 JBASE=JBASE+JUMP DO 80 K=LA1,M,LA KB=K+K-2 KC=KB+KB C1=TRIGS(KB+1) S1=TRIGS(KB+2) C2=TRIGS(KC+1) S2=TRIGS(KC+2) DO 70 L=1,LA I=IBASE J=JBASE DO 65 IJK=1,LOT C(JA+J)=A(IA+I)+(A(IB+I)+A(IC+I)) D(JA+J)=B(IA+I)+(B(IB+I)+B(IC+I)) C(JB+J)= * C1*((A(IA+I)-0.5*(A(IB+I)+A(IC+I))) X -(SIN60*(B(IB+I)-B(IC+I)))) * -S1*((B(IA+I)-0.5*(B(IB+I)+B(IC+I))) X +(SIN60*(A(IB+I)-A(IC+I)))) D(JB+J)= * S1*((A(IA+I)-0.5*(A(IB+I)+A(IC+I))) X -(SIN60*(B(IB+I)-B(IC+I)))) * +C1*((B(IA+I)-0.5*(B(IB+I)+B(IC+I))) X +(SIN60*(A(IB+I)-A(IC+I)))) C(JC+J)= * C2*((A(IA+I)-0.5*(A(IB+I)+A(IC+I))) X +(SIN60*(B(IB+I)-B(IC+I)))) * -S2*((B(IA+I)-0.5*(B(IB+I)+B(IC+I))) X -(SIN60*(A(IB+I)-A(IC+I)))) D(JC+J)= * S2*((A(IA+I)-0.5*(A(IB+I)+A(IC+I))) X +(SIN60*(B(IB+I)-B(IC+I)))) * +C2*((B(IA+I)-0.5*(B(IB+I)+B(IC+I))) X -(SIN60*(A(IB+I)-A(IC+I)))) I=I+INC3 J=J+INC4 65 CONTINUE IBASE=IBASE+INC1 JBASE=JBASE+INC2 70 CONTINUE JBASE=JBASE+JUMP 80 CONTINUE RETURN C C CODING FOR FACTOR 4 C 90 IA=1 JA=1 IB=IA+IINK JB=JA+JINK IC=IB+IINK JC=JB+JINK ID=IC+IINK JD=JC+JINK DO 100 L=1,LA I=IBASE J=JBASE DO 95 IJK=1,LOT C(JA+J)=(A(IA+I)+A(IC+I))+(A(IB+I)+A(ID+I)) C(JC+J)=(A(IA+I)+A(IC+I))-(A(IB+I)+A(ID+I)) D(JA+J)=(B(IA+I)+B(IC+I))+(B(IB+I)+B(ID+I)) D(JC+J)=(B(IA+I)+B(IC+I))-(B(IB+I)+B(ID+I)) C(JB+J)=(A(IA+I)-A(IC+I))-(B(IB+I)-B(ID+I)) C(JD+J)=(A(IA+I)-A(IC+I))+(B(IB+I)-B(ID+I)) D(JB+J)=(B(IA+I)-B(IC+I))+(A(IB+I)-A(ID+I)) D(JD+J)=(B(IA+I)-B(IC+I))-(A(IB+I)-A(ID+I)) I=I+INC3 J=J+INC4 95 CONTINUE IBASE=IBASE+INC1 JBASE=JBASE+INC2 100 CONTINUE IF (LA.EQ.M) RETURN LA1=LA+1 JBASE=JBASE+JUMP DO 120 K=LA1,M,LA KB=K+K-2 KC=KB+KB KD=KC+KB C1=TRIGS(KB+1) S1=TRIGS(KB+2) C2=TRIGS(KC+1) S2=TRIGS(KC+2) C3=TRIGS(KD+1) S3=TRIGS(KD+2) DO 110 L=1,LA I=IBASE J=JBASE DO 105 IJK=1,LOT C(JA+J)=(A(IA+I)+A(IC+I))+(A(IB+I)+A(ID+I)) D(JA+J)=(B(IA+I)+B(IC+I))+(B(IB+I)+B(ID+I)) C(JC+J)= * C2*((A(IA+I)+A(IC+I))-(A(IB+I)+A(ID+I))) * -S2*((B(IA+I)+B(IC+I))-(B(IB+I)+B(ID+I))) D(JC+J)= * S2*((A(IA+I)+A(IC+I))-(A(IB+I)+A(ID+I))) * +C2*((B(IA+I)+B(IC+I))-(B(IB+I)+B(ID+I))) C(JB+J)= * C1*((A(IA+I)-A(IC+I))-(B(IB+I)-B(ID+I))) * -S1*((B(IA+I)-B(IC+I))+(A(IB+I)-A(ID+I))) D(JB+J)= * S1*((A(IA+I)-A(IC+I))-(B(IB+I)-B(ID+I))) * +C1*((B(IA+I)-B(IC+I))+(A(IB+I)-A(ID+I))) C(JD+J)= * C3*((A(IA+I)-A(IC+I))+(B(IB+I)-B(ID+I))) * -S3*((B(IA+I)-B(IC+I))-(A(IB+I)-A(ID+I))) D(JD+J)= * S3*((A(IA+I)-A(IC+I))+(B(IB+I)-B(ID+I))) * +C3*((B(IA+I)-B(IC+I))-(A(IB+I)-A(ID+I))) I=I+INC3 J=J+INC4 105 CONTINUE IBASE=IBASE+INC1 JBASE=JBASE+INC2 110 CONTINUE JBASE=JBASE+JUMP 120 CONTINUE RETURN C C CODING FOR FACTOR 5 C 130 IA=1 JA=1 IB=IA+IINK JB=JA+JINK IC=IB+IINK JC=JB+JINK ID=IC+IINK JD=JC+JINK IE=ID+IINK JE=JD+JINK DO 140 L=1,LA I=IBASE J=JBASE DO 135 IJK=1,LOT C(JA+J)=A(IA+I)+(A(IB+I)+A(IE+I))+(A(IC+I)+A(ID+I)) D(JA+J)=B(IA+I)+(B(IB+I)+B(IE+I))+(B(IC+I)+B(ID+I)) C(JB+J)=(A(IA+I)+COS72*(A(IB+I)+A(IE+I))-COS36*(A(IC+I)+A(ID+I))) * -(SIN72*(B(IB+I)-B(IE+I))+SIN36*(B(IC+I)-B(ID+I))) C(JE+J)=(A(IA+I)+COS72*(A(IB+I)+A(IE+I))-COS36*(A(IC+I)+A(ID+I))) * +(SIN72*(B(IB+I)-B(IE+I))+SIN36*(B(IC+I)-B(ID+I))) D(JB+J)=(B(IA+I)+COS72*(B(IB+I)+B(IE+I))-COS36*(B(IC+I)+B(ID+I))) * +(SIN72*(A(IB+I)-A(IE+I))+SIN36*(A(IC+I)-A(ID+I))) D(JE+J)=(B(IA+I)+COS72*(B(IB+I)+B(IE+I))-COS36*(B(IC+I)+B(ID+I))) * -(SIN72*(A(IB+I)-A(IE+I))+SIN36*(A(IC+I)-A(ID+I))) C(JC+J)=(A(IA+I)-COS36*(A(IB+I)+A(IE+I))+COS72*(A(IC+I)+A(ID+I))) * -(SIN36*(B(IB+I)-B(IE+I))-SIN72*(B(IC+I)-B(ID+I))) C(JD+J)=(A(IA+I)-COS36*(A(IB+I)+A(IE+I))+COS72*(A(IC+I)+A(ID+I))) * +(SIN36*(B(IB+I)-B(IE+I))-SIN72*(B(IC+I)-B(ID+I))) D(JC+J)=(B(IA+I)-COS36*(B(IB+I)+B(IE+I))+COS72*(B(IC+I)+B(ID+I))) * +(SIN36*(A(IB+I)-A(IE+I))-SIN72*(A(IC+I)-A(ID+I))) D(JD+J)=(B(IA+I)-COS36*(B(IB+I)+B(IE+I))+COS72*(B(IC+I)+B(ID+I))) * -(SIN36*(A(IB+I)-A(IE+I))-SIN72*(A(IC+I)-A(ID+I))) I=I+INC3 J=J+INC4 135 CONTINUE IBASE=IBASE+INC1 JBASE=JBASE+INC2 140 CONTINUE IF (LA.EQ.M) RETURN LA1=LA+1 JBASE=JBASE+JUMP DO 160 K=LA1,M,LA KB=K+K-2 KC=KB+KB KD=KC+KB KE=KD+KB C1=TRIGS(KB+1) S1=TRIGS(KB+2) C2=TRIGS(KC+1) S2=TRIGS(KC+2) C3=TRIGS(KD+1) S3=TRIGS(KD+2) C4=TRIGS(KE+1) S4=TRIGS(KE+2) DO 150 L=1,LA I=IBASE J=JBASE DO 145 IJK=1,LOT C(JA+J)=A(IA+I)+(A(IB+I)+A(IE+I))+(A(IC+I)+A(ID+I)) D(JA+J)=B(IA+I)+(B(IB+I)+B(IE+I))+(B(IC+I)+B(ID+I)) C(JB+J)= * C1*((A(IA+I)+COS72*(A(IB+I)+A(IE+I))-COS36*(A(IC+I)+A(ID+I))) * -(SIN72*(B(IB+I)-B(IE+I))+SIN36*(B(IC+I)-B(ID+I)))) * -S1*((B(IA+I)+COS72*(B(IB+I)+B(IE+I))-COS36*(B(IC+I)+B(ID+I))) * +(SIN72*(A(IB+I)-A(IE+I))+SIN36*(A(IC+I)-A(ID+I)))) D(JB+J)= * S1*((A(IA+I)+COS72*(A(IB+I)+A(IE+I))-COS36*(A(IC+I)+A(ID+I))) * -(SIN72*(B(IB+I)-B(IE+I))+SIN36*(B(IC+I)-B(ID+I)))) * +C1*((B(IA+I)+COS72*(B(IB+I)+B(IE+I))-COS36*(B(IC+I)+B(ID+I))) * +(SIN72*(A(IB+I)-A(IE+I))+SIN36*(A(IC+I)-A(ID+I)))) C(JE+J)= * C4*((A(IA+I)+COS72*(A(IB+I)+A(IE+I))-COS36*(A(IC+I)+A(ID+I))) * +(SIN72*(B(IB+I)-B(IE+I))+SIN36*(B(IC+I)-B(ID+I)))) * -S4*((B(IA+I)+COS72*(B(IB+I)+B(IE+I))-COS36*(B(IC+I)+B(ID+I))) * -(SIN72*(A(IB+I)-A(IE+I))+SIN36*(A(IC+I)-A(ID+I)))) D(JE+J)= * S4*((A(IA+I)+COS72*(A(IB+I)+A(IE+I))-COS36*(A(IC+I)+A(ID+I))) * +(SIN72*(B(IB+I)-B(IE+I))+SIN36*(B(IC+I)-B(ID+I)))) * +C4*((B(IA+I)+COS72*(B(IB+I)+B(IE+I))-COS36*(B(IC+I)+B(ID+I))) * -(SIN72*(A(IB+I)-A(IE+I))+SIN36*(A(IC+I)-A(ID+I)))) C(JC+J)= * C2*((A(IA+I)-COS36*(A(IB+I)+A(IE+I))+COS72*(A(IC+I)+A(ID+I))) * -(SIN36*(B(IB+I)-B(IE+I))-SIN72*(B(IC+I)-B(ID+I)))) * -S2*((B(IA+I)-COS36*(B(IB+I)+B(IE+I))+COS72*(B(IC+I)+B(ID+I))) * +(SIN36*(A(IB+I)-A(IE+I))-SIN72*(A(IC+I)-A(ID+I)))) D(JC+J)= * S2*((A(IA+I)-COS36*(A(IB+I)+A(IE+I))+COS72*(A(IC+I)+A(ID+I))) * -(SIN36*(B(IB+I)-B(IE+I))-SIN72*(B(IC+I)-B(ID+I)))) * +C2*((B(IA+I)-COS36*(B(IB+I)+B(IE+I))+COS72*(B(IC+I)+B(ID+I))) * +(SIN36*(A(IB+I)-A(IE+I))-SIN72*(A(IC+I)-A(ID+I)))) C(JD+J)= * C3*((A(IA+I)-COS36*(A(IB+I)+A(IE+I))+COS72*(A(IC+I)+A(ID+I))) * +(SIN36*(B(IB+I)-B(IE+I))-SIN72*(B(IC+I)-B(ID+I)))) * -S3*((B(IA+I)-COS36*(B(IB+I)+B(IE+I))+COS72*(B(IC+I)+B(ID+I))) * -(SIN36*(A(IB+I)-A(IE+I))-SIN72*(A(IC+I)-A(ID+I)))) D(JD+J)= * S3*((A(IA+I)-COS36*(A(IB+I)+A(IE+I))+COS72*(A(IC+I)+A(ID+I))) * +(SIN36*(B(IB+I)-B(IE+I))-SIN72*(B(IC+I)-B(ID+I)))) * +C3*((B(IA+I)-COS36*(B(IB+I)+B(IE+I))+COS72*(B(IC+I)+B(ID+I))) * -(SIN36*(A(IB+I)-A(IE+I))-SIN72*(A(IC+I)-A(ID+I)))) I=I+INC3 J=J+INC4 145 CONTINUE IBASE=IBASE+INC1 JBASE=JBASE+INC2 150 CONTINUE JBASE=JBASE+JUMP 160 CONTINUE RETURN END SUBROUTINE FFT99M(A,WORK,TRIGS,IFAX,INC,JUMP,N,LOT,ISIGN) SAVE DIMENSION A(N),WORK(N),TRIGS(N),IFAX(1) C NFAX=IFAX(1) NX=N NH=N/2 INK=INC+INC IF (ISIGN.EQ.+1) GO TO 30 C C IF NECESSARY, TRANSFER DATA TO WORK AREA IGO=50 IF (MOD(NFAX,2).EQ.1) GOTO 40 IBASE=1 JBASE=1 DO 20 L=1,LOT I=IBASE J=JBASE DO 10 M=1,N WORK(J)=A(I) I=I+INC J=J+1 10 CONTINUE IBASE=IBASE+JUMP JBASE=JBASE+NX 20 CONTINUE C IGO=60 GO TO 40 C C PREPROCESSING (ISIGN=+1) C ------------------------ C 30 CONTINUE CALL FFT99A(A,WORK,TRIGS,INC,JUMP,N,LOT) IGO=60 C C COMPLEX TRANSFORM C ----------------- C 40 CONTINUE IA=1 LA=1 DO 80 K=1,NFAX IF (IGO.EQ.60) GO TO 60 50 CONTINUE CALL VPASSM(A(IA),A(IA+INC),WORK(1),WORK(2),TRIGS, * INK,2,JUMP,NX,LOT,NH,IFAX(K+1),LA) IGO=60 GO TO 70 60 CONTINUE CALL VPASSM(WORK(1),WORK(2),A(IA),A(IA+INC),TRIGS, * 2,INK,NX,JUMP,LOT,NH,IFAX(K+1),LA) IGO=50 70 CONTINUE LA=LA*IFAX(K+1) 80 CONTINUE C IF (ISIGN.EQ.-1) GO TO 130 C C IF NECESSARY, TRANSFER DATA FROM WORK AREA IF (MOD(NFAX,2).EQ.1) GO TO 110 IBASE=1 JBASE=1 DO 100 L=1,LOT I=IBASE J=JBASE DO 90 M=1,N A(J)=WORK(I) I=I+1 J=J+INC 90 CONTINUE IBASE=IBASE+NX JBASE=JBASE+JUMP 100 CONTINUE C C FILL IN ZEROS AT END 110 CONTINUE GO TO 140 C C POSTPROCESSING (ISIGN=-1): C -------------------------- C 130 CONTINUE CALL FFT99B(WORK,A,TRIGS,INC,JUMP,N,LOT) C 140 CONTINUE RETURN END SUBROUTINE FFT99A(A,WORK,TRIGS,INC,JUMP,N,LOT) SAVE C SUBROUTINE FFT99A - PREPROCESSING STEP FOR FFT99, ISIGN=+1 C (SPECTRAL TO GRIDPOINT TRANSFORM) C DIMENSION A(N),WORK(N),TRIGS(N) C NH=N/2 NX=N INK=INC+INC C C A(0) A(N/2) IA=1 IB=N*INC+1 JA=1 JB=2 DO 10 L=1,LOT WORK(JA)=A(IA) WORK(JB)=A(IA) IA=IA+JUMP IB=IB+JUMP JA=JA+NX JB=JB+NX 10 CONTINUE C C REMAINING WAVENUMBERS IABASE=2*INC+1 IBBASE=(N-2)*INC+1 JABASE=3 JBBASE=N-1 C DO 30 K=3,NH,2 IA=IABASE IB=IBBASE JA=JABASE JB=JBBASE C=TRIGS(N+K) S=TRIGS(N+K+1) DO 20 L=1,LOT WORK(JA)=(A(IA)+A(IB))- * (S*(A(IA)-A(IB))+C*(A(IA+INC)+A(IB+INC))) WORK(JB)=(A(IA)+A(IB))+ * (S*(A(IA)-A(IB))+C*(A(IA+INC)+A(IB+INC))) WORK(JA+1)=(C*(A(IA)-A(IB))-S*(A(IA+INC)+A(IB+INC)))+ * (A(IA+INC)-A(IB+INC)) WORK(JB+1)=(C*(A(IA)-A(IB))-S*(A(IA+INC)+A(IB+INC)))- * (A(IA+INC)-A(IB+INC)) IA=IA+JUMP IB=IB+JUMP JA=JA+NX JB=JB+NX 20 CONTINUE IABASE=IABASE+INK IBBASE=IBBASE-INK JABASE=JABASE+2 JBBASE=JBBASE-2 30 CONTINUE C IF (IABASE.NE.IBBASE) GO TO 50 C WAVENUMBER N/4 (IF IT EXISTS) IA=IABASE JA=JABASE DO 40 L=1,LOT WORK(JA)=2.0*A(IA) WORK(JA+1)=-2.0*A(IA+INC) IA=IA+JUMP JA=JA+NX 40 CONTINUE C 50 CONTINUE RETURN END SUBROUTINE FFT99B(WORK,A,TRIGS,INC,JUMP,N,LOT) SAVE C SUBROUTINE FFT99B - POSTPROCESSING STEP FOR FFT99, ISIGN=-1 C (GRIDPOINT TO SPECTRAL TRANSFORM) C DIMENSION WORK(N),A(N),TRIGS(N) C NH=N/2 NX=N INK=INC+INC C C A(0) A(N/2) SCALE=1.0/FLOAT(N) IA=1 IB=2 JA=1 JB=N*INC+1 DO 10 L=1,LOT A(JA)=SCALE*(WORK(IA)+WORK(IB)) A(JA+INC)=0.0 IA=IA+NX IB=IB+NX JA=JA+JUMP JB=JB+JUMP 10 CONTINUE C C REMAINING WAVENUMBERS SCALE=0.5*SCALE IABASE=3 IBBASE=N-1 JABASE=2*INC+1 JBBASE=(N-2)*INC+1 C DO 30 K=3,NH,2 IA=IABASE IB=IBBASE JA=JABASE JB=JBBASE C=TRIGS(N+K) S=TRIGS(N+K+1) DO 20 L=1,LOT A(JA)=SCALE*((WORK(IA)+WORK(IB)) * +(C*(WORK(IA+1)+WORK(IB+1))+S*(WORK(IA)-WORK(IB)))) A(JB)=SCALE*((WORK(IA)+WORK(IB)) * -(C*(WORK(IA+1)+WORK(IB+1))+S*(WORK(IA)-WORK(IB)))) A(JA+INC)=SCALE*((C*(WORK(IA)-WORK(IB))-S*(WORK(IA+1)+WORK(IB+1))) * +(WORK(IB+1)-WORK(IA+1))) A(JB+INC)=SCALE*((C*(WORK(IA)-WORK(IB))-S*(WORK(IA+1)+WORK(IB+1))) * -(WORK(IB+1)-WORK(IA+1))) IA=IA+NX IB=IB+NX JA=JA+JUMP JB=JB+JUMP 20 CONTINUE IABASE=IABASE+2 IBBASE=IBBASE-2 JABASE=JABASE+INK JBBASE=JBBASE-INK 30 CONTINUE C IF (IABASE.NE.IBBASE) GO TO 50 C WAVENUMBER N/4 (IF IT EXISTS) IA=IABASE JA=JABASE SCALE=2.0*SCALE DO 40 L=1,LOT A(JA)=SCALE*WORK(IA) A(JA+INC)=-SCALE*WORK(IA+1) IA=IA+NX JA=JA+JUMP 40 CONTINUE C 50 CONTINUE RETURN END