SUBROUTINE MFFTDM(C,IMSX,IVSX,IESX,NMX,NVX,NEX,TABLES,IERR)*   PURPOSE:*       THIS SUBROUTINE PERFORMS A DIRECT FOURIER TRANSFORM ALONG*       THE SECOND DIMENSION OF A 3-DIMENSIONAL MATRIX, USING THE*       GENTLEMAN-SANDE ALGORITHM.*       THE SEQUENCE TO BE TRANSFORMED IS C[IMSX,NMX], WHOSE COMPONENTS*       ARE THE 2-VECTORS C(M)[IVSX,NVX [IESX,NEX]].*       SEE REF.[1] FOR NOTATIONS.*  EXAMPLE:*       LET C BE A 3-D MATRIX C(N1,N2,N3), DECLARED VIA*              DIMENSION C(NN1,N2,N3)*       WITH NN1.GE.N1*       THEN ITS DFT ALONG THE SECOND DIMENSION IS OBTAINED BY*              CALL MFFTDM(C,NN1,NN1*N2,1,N2,N3,N1,TABLES,IERR)*  IMPLEMENTATION:*       THE TRANSFORMATION IS IMPLEMENTED THROUGH REPEATED CALLS TO THE*       "BUTTERFLY" TRANSFORMATION MFFT?6; PARAMETERS OF THE "BUTTERFLY"*       ARE COMMUNICATED THROUGH THE COMMON BLOCK MFFTPA.*  ARGUMENTS:*    INPUT  :*       C : ARRAY TO BE TRANSFORMED.*       IMSX,IVSX,IESX,NMX,NVX,NEX: THESE ARGUMENTS DEFINE THE STRUCTURE*           OF C ACCORDING TO THE DEFINITIONS ABOVE. THEY ARE UNCHANGED*           ON OUTPUT*       TABLES : ARRAY PREPARED BY MFFTP. IT  IS NOT CHANGED ON OUTPUT.*                IT SHOULD BE DECLARED INTEGER TABLES(4*NM+14);*                IT MUST BE INITIALIZED BY MFFTP BEFORE USAGE.*    OUTPUT:*       C : TRANSFORM OF THE ORIGINAL ARRAY; "BIT REVERSED" ORDER*       IERR : ERROR CODE : =0 : SUCCESSFUL*                         : =3 :  'TABLES' NOT CORRECTLY INITIALIZED      COMPLEX C(*)      INTEGER TABLES(-14:*)      INTEGER IDERR,FACERR,TBERR      PARAMETER (IDERR=1,FACERR=2,TBERR=3)      COMMON /MFFTPA/  IMS,IVS,IES,NM,NV,NE,MX,LX,MLIM,MSTEP,LLIM,LSTEP,     $ NUSTEP,IVLIM,ILIM,MD2LIM,LD2LIM*  LOADING THE COMMON BLOCK : CONSTANTS      IMS=IMSX      IVS=IVSX      IES=IESX      NM=NMX      NV=NVX      NE=NEX       IVLIM=(NV-1)*IVS      ILIM=(NE-1)*IES      MSTEP=IMS*  LOADING THE COMMON BLOCK : ITERATION-DEPENDENT QUANTITIES: INITIALIZA      LX=1      MX=NM*  SELECT THE HIGHEST FACTOR OF NM      IFAC=TABLES(-1)      GOTO(200,300,500)IFAC      IERR=TBERR      RETURN*...  RADIX 5 LOOP500   CONTINUE      DO 510 IM=1,TABLES(-12)        MX=MX/5        NUSTEP=MX*MSTEP        MLIM=NUSTEP-MSTEP        LSTEP=NUSTEP*5        LLIM=NM*MSTEP-LSTEP        CALL MFFTC6(C,TABLES(0))        LX=LX*5510   CONTINUE*..  RADIX 3 LOOP300   CONTINUE      DO 310 IM=1,TABLES(-13)        MX=MX/3        NUSTEP=MX*MSTEP        MLIM=NUSTEP-MSTEP        LSTEP=NUSTEP*3        LLIM=NM*MSTEP-LSTEP        CALL MFFTB6(C,TABLES(0))        LX=LX*3310   CONTINUE*..  RADIX 2 LOOP200   CONTINUE      DO 210 IM=1,TABLES(-14)        MX=MX/2        NUSTEP=MX*MSTEP        MLIM=NUSTEP-MSTEP        MD2LIM=NUSTEP/2-MSTEP        LSTEP=NUSTEP*2        LLIM=NM*MSTEP-LSTEP        CALL MFFTA6(C,TABLES(0))        LX=LX+LX210   CONTINUE      END