DZFFT Routine Documentation

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

SUBROUTINE

INTEGER MODE

Input

The value of MODE on input determines the operation performed by DZFFT. 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. MODE=1 : a real transform is performed. Initializations are assumed to have been performed by a prior call to DZFFT. MODE=2 : initializations and a real transform are performed.

INTEGER N

Input

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

DOUBLE PRECISION X(N)

Input/Output

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

DOUBLE PRECISION 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 DZFFT(0,N,X,COMM,INFO)
             CALL DZFFT(1,N,X,COMM,INFO)
             DO 10 I = N/2+2, N
                X(I) = -X(I)
        10   CONTINUE
             CALL ZDFFT(1,N,X,COMM,INFO)