SUBROUTINE C2FFT(C,ID,NM,NN,WM,WN,ISIG,IORD,IWORK,IERR)****PURPOSE:*       THIS ROUTINE PERFORMS A 2-DIMENSIONAL COMPLEX FOURIER TRANSFORM,*       OF ORDER NM*NN.****USAGE:*       THE USER IS EXPECTED TO PROVIDE THE DATA IN A 2-DIMENSIONAL*       COMPLEX ARRAY C, DIMENSIONED IN THE CALLING PROGRAM C(ID,NN);*       ID CAN BE DIFFERENT FROM NM, AND IT IS RECOMMENDED THAT IT IS*       CHOSEN EQUAL TO NM+1 IF NM IS EVEN OR TO NM IF NM IS ODD.*       THE ELEMENTS C(K,*),NM<K<=ID MUST BE ZEROED. THE ROUTINE IS*       INTENDED FOR REPEATED USAGE, THUS SEPARATE SET-UP AND*       OPERATING CALLS ARE AVAILABLE : THE USER SHOULD ALWAYS PERFORM*       A SET-UP CALL ( ISIG=0 ) PASSING THE CHOSEN PARAMETERS, BEFORE*       PERFORMING THE ACTUAL TRANSFORM ( ISIG= +1 OR -1 ); THE USER CAN*       CHOOSE WHETHER TO OBTAIN THE RESULTS OF THE DIRECT TRANSFORM*       IN NATURAL ORDER (ISIG=-1,IORD=1) OR LEAVE THEM IN THE*      'BIT-REVERSED' ORDER( ISIG=-1,IORD=0); THIS CHOICE SAVES*       SOME COMPUTER TIME, AND IT IS RECOMMENDED IN CASES DISCUSSED*       IN THE LONG WRITE-UP. ANALOGOUSLY,THE INVERSE TRANSFORM ACCEPTS*       INPUT ( PLEASE NOTE| ) DATA IN NATURAL ORDER ( ISIG=1,IORD=1),*       OR DATA ALREADY SUBJECTED TO A BIT-REVERSAL PERMUTATION( ISIG=1*       IORD=0 ).****PARAMETERS :*       INPUT :*       C : ARRAY TO BE TRANSFORMED; DECLARED COMPLEX C(ID,NN) IN THE*           CALLING PROGRAM;*       ID : FIRST DIMENSION OF C IN THE CALLING PROGRAM*       ISIG : OPTION FLAG : ISIG=0 : SET-UP RUN, C NOT USED*                            ISIG=-1: DIRECT TRANSFORM*                            ISIG=+1: INVERSE TRANSFORM*       WM,WN : INTEGER ARRAYS , USED TO HOST TABLES FOR THE TRANSFORM;*               DIMENSIONED IN THE CALLING PROGRAM AT LEAST (4*NM+14)*               AND (4*NN+14) RESPECTIVELY; IF ISIG.NE.0 ,THEY ARE*               ASSUMED TO HAVE BEEN SET BY A PREVIOUS CALL WITH ISIG=0*               (ALL OTHER ARGUMENTS UNCHANGED), AND NEVER HAVE BEEN*               MODIFIED SINCE THEN;*               IF NM=NN, WM AND WN DO NOT NEED TO BE DISTINCT;*       NM : ORDER OF THE TRANSFORM ALONG THE COLUMNS OF C*       NN : ORDER OF THE TRANSFORM ALONG THE ROWS OF C*       IORD : OPTION FLAG : =1 : OUTPUT IN NATURAL ORDER (ISIG=-1)*                                 INPUT IN NATURAL ORDER  (ISIG=+1)*                            =0 : OUTPUT IN BIT-REVERSED ORDER(ISIG=-1)*                                 INPUT IN BIT-REVERSED ORDER(ISIG=+1)*       IWORK : INTEGER ARRAY, USED AS WORK AREA FOR REORDERING IF IORD=*                1, IT MUST BE AT LEAST MAX(NM,NN) WORDS LONG.*                IT IS UNUSED IF IORD=0.*****OUTPUT :*       C : TRANSFORMED ARRAY*       WM, WN : ONLY IF ISIG=0, WM AND WN ARE FILLED WITH THE*               APPROPRIATE  TABLES (TWIDDLE FACTORS).*       IWORK : UNDEFINED*       IERR  : ERROR CODE : =0 : SUCCESSFUL*                            =1 : DATA DIMENSIONS ARE NOT CORRECT*                            =2 : PRIME FACTORS DIFFERENT FROM 2,3,5*                                 ARE PRESENT IN DATA DIMENSIONS*                            =3 : TABLES NOT CORRECTLY INITIALIZED*      COMPLEX C(*)      INTEGER WM(-14:*),WN(-14:*)      INTEGER IWORK(*)      INTEGER IDERR,FACERR,TBERR      PARAMETER (IDERR=1,FACERR=2,TBERR=3)      IF(ID.LT.NM)THEN        IERR=IDERR        RETURN      ENDIF      IERR=0      IF(ISIG.EQ.0)THEN        CALL MFFTP(NM,WM,0,IERR)        IF(IERR.NE.0)RETURN        IF(NN.NE.NM)THEN          CALL MFFTP(NN,WN,0,IERR)          IF(IERR.NE.0)RETURN        ELSE          CALL MFFTZ0(WM,1,4*NM+14,WN,1)        ENDIF        RETURN       ELSE IF(ISIG.GT.0)THEN         IF(IORD.NE.0)THEN         CALL MFFTOV(C,1,ID,NM,NN,WM(3*NM),IWORK)         CALL MFFTOV(C,ID,1,NN,NM,WN(3*NN),IWORK)        ENDIF         CALL MFFTIV(C,1,ID,NM,NN,WM,IERR)        IF(IERR.NE.0)RETURN        CALL MFFTIV(C,ID,1,NN,NM,WN,IERR)        IF(IERR.NE.0)RETURN       ELSE        CALL MFFTDV(C,1,ID,NM,NN,WM,IERR)        IF(IERR.NE.0)RETURN        CALL MFFTDV(C,ID,1,NN,NM,WN,IERR)        IF(IERR.NE.0)RETURN         IF(IORD.NE.0)THEN         CALL MFFTOV(C,1,ID,NM,NN,WM(2*NM),IWORK)         CALL MFFTOV(C,ID,1,NN,NM,WN(2*NN),IWORK)        ENDIF      ENDIF       END