EZ Fourier Transform

Calling Sequence

CALL EZFFTF	(N, R, AZERO, A, B, WSAVE)
void ezfftf	(int n, float *r, float *azero, float *a, float *b, float *wsave)

Arguments

N	Length of the sequence to be transformed. The method is most efficient when N is the product of small primes. N 0.
R	A real array of length N containing the sequence to be transformed. On exit, R is unchanged.
AZERO	The sum from i=1 to i=n of r(i)/n
A, B	For N even, and For N even, define kmax=n/2-1 and for N odd, define kmax=(n-1)/2, then for k=1,...,kmax
xWSAVE	On entry, an array with dimension of at least (3 × N + 15), initialized by EZFFTI.

Sample Program

PROGRAM TEST

IMPLICIT NONE

C

INTEGER N

PARAMETER (N = 9)

C

INTEGER I

REAL A(N), B(N), AZERO, PI, R(N)

REAL WSAVE(3 * N + 15)

C

EXTERNAL EZFFTB, EZFFTF, EZFFTI

INTRINSIC ACOS, COS, SIN

C

C Initialize array to a sequence of real numbers.

C

PI = ACOS (-1.0)

DO 100, I=1, N

R(I) = 3.0 + SIN ((I - 1.0) * 2.0 * PI / N) +

$ 4.0 * COS ((I - 1.0) * 8.0 * PI / N)

100 CONTINUE

C

CALL EZFFTI (N, WSAVE)

PRINT 1000

PRINT 1010, (R(I), I = 1, N)

CALL EZFFTF (N, R, AZERO, A, B, WSAVE)

PRINT 1020, AZERO

PRINT 1030

PRINT 1010, (A(I), I = 1, N)

PRINT 1040

PRINT 1010, (B(I), I = 1, N)

CALL EZFFTB (N, R, AZERO, A, B, WSAVE)

PRINT 1050

PRINT 1010, (R(I), I = 1, N)

C

1000 FORMAT (1X, 'Original Sequence: ')

1010 FORMAT (100(F6.1, 1X))

1020 FORMAT (1X, 'Azero = ' F4.1)

1030 FORMAT (1X, 'A = ')

1040 FORMAT (1X, 'B = ')

1050 FORMAT (1X, 'Recovered Sequence: ')

C

END

Sample Output

Original Sequence:
7.0 -0.1 7.0 1.9 4.0 3.4 0.1 5.1 -1.4
Azero = 3.0
A =
0.0 0.0 0.0 4.0 0.0 0.0 0.0 0.0 0.0
B =
1.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Recovered Sequence:
7.0 -0.1 7.0 1.9 4.0 3.4 0.1 5.1 -1.4