SUBROUTINE MFFTB4(C,FAC)**   PURPOSE:*       ELEMENTARY GENTLEMAN-SANDE RADIX 3 STEP APPLIED TO A VECTOR-OF*       VECTORS-OF-COMPLEX C[IVS,NV [IES,NE]].*       SEE REF.[1] FOR NOTATIONS.*       THIS ROUTINE CAN BE USED ONLY BY ROUTINE MFFTDV, 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-1,0:2),FAC(0:*)      COMPLEX T0,T1,T2,F1,F2       REAL SIN60      PARAMETER ( SIN60 =  8.6602540378443864E-1) *..  MU > 1            MUF=LX            DO 200 MU=MSTEP,MLIM,MSTEP              F1=CONJG(FAC(MUF))              F2=CONJG(FAC(2*MUF))              DO 190 LAM=MU,MU+LLIM,LSTEP                DO 180 I=LAM,LAM+ILIM,IES                T0=C(I,1)+C(I,2)                T1=C(I,0)-0.5*T0                T2=(C(I,1)-C(I,2))*SIN60                C(I,0)=C(I,0)+T0                C(I,1)=(T1-CMPLX(-AIMAG(T2),REAL(T2)))*F1                C(I,2)=(T1+CMPLX(-AIMAG(T2),REAL(T2)))*F2  180           CONTINUE  190         CONTINUE              MUF=MUF+LX200         CONTINUE *..  MU=01000        DO 193 LAM=0,LLIM,LSTEP              DO 183 I=LAM,LAM+ILIM,IES                T0=C(I,1)+C(I,2)                T1=C(I,0)-0.5*T0                T2=(C(I,1)-C(I,2))*SIN60                C(I,0)=C(I,0)+T0                C(I,1)=(T1-CMPLX(-AIMAG(T2),REAL(T2)))                C(I,2)=(T1+CMPLX(-AIMAG(T2),REAL(T2)))183           CONTINUE193         CONTINUE      END