ZFFT1D Routine Documentation

ZFFT1D (MODE,N,X,COMM,INFO)

SUBROUTINE

INTEGER MODE

Input

The value of MODE on input determines the operation performed by ZFFT1D. On input: MODE=0 : only initializations (specific to the value of N) are performed; this is usually followed by calls to the same routine with MODE=-1 or 1. MODE=-1 : a forward transform is performed. Initializations are assumed to have been performed by a prior call to ZFFT1D. MODE=1 : a backward (reverse) transform is performed. Initializations are assumed to have been performed by a prior call to ZFFT1D. MODE=-2 : initializations and a forward transform are performed. MODE=2 : initializations and a backward transform are performed.

INTEGER N

Input

On input: N is the length of the complex sequence X

COMPLEX*16 X(N)

Input/Output

On input: X contains the complex sequence of length N to be transformed. On output: X contains the transformed sequence.

COMPLEX*16 COMM(3*N+100)

Input/Output

COMM is a communication array. Some portions of the array are used to store initializations for subsequent calls with the same sequence length N. The remainder is used as temporary store.

INTEGER INFO

Output

On output: INFO is an error indicator. On successful exit, INFO contains 0. If INFO = -i on exit, the i-th argument had an illegal value.

     Example:
             CALL ZFFT1D(0,N,X,COMM,INFO)
             CALL ZFFT1D(-1,N,X,COMM,INFO)
             CALL ZFFT1D(-1,N,Y,COMM,INFO)
             DO 10 I = 1, N
                X(I) = X(I)*DCONJG(Y(I))
        10   CONTINUE
             CALL ZFFT1D(1,N,X,COMM,INFO)