SUBROUTINE MFFTB9(C,FAC)**   PURPOSE:*       ELEMENTARY COOLEY-TUKEY RADIX 3 STEP APPLIED TO A VECTOR-OF*       2-VECTORS-OF-COMPLEX C[IMS,NM [IVS,NV [IES,NE]]].*       SEE REF.[1] FOR NOTATIONS.*       THIS ROUTINE CAN BE USED ONLY BY ROUTINE MFFTIM, WHICH CONTROLS*       ITS OPERATION THROUGH THE MFFTPA COMMON**   DUMMY ARGUMENTS :**   C   ARRAY BEING FOURIER  TRANSFORMED*   FAC PHASE FACTORS, PREPARED BY MFFTP; NOT MODIFIED IN OUTPUT*      COMMON /MFFTPA/  IMS,IVS,IES,NM,NV,NE,MX,LX,MLIM,MSTEP,LLIM,LSTEP,     $ NUSTEP,IVLIM,ILIM,MD2LIM,LD2LIM      INTEGER NUSTEP      COMPLEX C(0:NUSTEP-1,0:1),FAC(0:*)      COMPLEX T0,T1,T2,F1,F2      REAL SIN60      PARAMETER ( SIN60 =  8.6602540378443864E-1)       IF(LX.NE.1)THEN          DO 200 MU=0,MLIM,MSTEP            DO 150 IV=MU,MU+IVLIM,IVS              ILAMF=0              DO 100 ILAM=IV,IV+ILIM                T0=C(ILAM,1)*FAC(ILAMF)+C(ILAM,2)*FAC(ILAMF+NUSTEP)                T2=(C(ILAM,1)*FAC(ILAMF)-C(ILAM,2)*FAC(ILAMF+NUSTEP))*     $             SIN60                T1=C(ILAM,0)-0.5*T0                C(ILAM,0)=C(ILAM,0)+T0                C(ILAM,1)=(T1+CMPLX(-AIMAG(T2),REAL(T2)))                C(ILAM,2)=(T1-CMPLX(-AIMAG(T2),REAL(T2)))                ILAMF=ILAMF+1100           CONTINUE150         CONTINUE200       CONTINUE      ELSE          DO 400 MU=0,MLIM,MSTEP            DO 350 IV=MU,MU+IVLIM,IVS              DO 300 ILAM=IV,IV+ILIM                T0=C(ILAM,1)+C(ILAM,2)                T2=(C(ILAM,1)-C(ILAM,2))*SIN60                T1=C(ILAM,0)-0.5*T0                C(ILAM,0)=C(ILAM,0)+T0                C(ILAM,1)=(T1+CMPLX(-AIMAG(T2),REAL(T2)))                C(ILAM,2)=(T1-CMPLX(-AIMAG(T2),REAL(T2)))300           CONTINUE350         CONTINUE400       CONTINUE      ENDIF      END