CFFT1D Routine Documentation

CFFT1D (MODE,N,X,COMM,INFO)

SUBROUTINE

INTEGER MODE

Input

The value of MODE on input determines the operation performed by CFFT1D. 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 CFFT1D. MODE=1 : a backward (reverse) transform is performed. Initializations are assumed to have been performed by a prior call to CFFT1D. 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 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 COMM(5*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 CFFT1D(0,N,X,COMM,INFO)
             CALL CFFT1D(-1,N,X,COMM,INFO)
             CALL CFFT1D(-1,N,Y,COMM,INFO)
             DO 10 I = 1, N
                X(I) = X(I)*CONJG(Y(I))
        10   CONTINUE
             CALL CFFT1D(1,N,X,COMM,INFO)