ezfftf(3P)

NAME

ezfftf - computes the Fourier coefficients of a perodic sequence. EZFFTF is a simplified but slower version of RFFTF.

SYNOPSIS

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

void ezfftf (long int n, float ∗r, float ∗azero, float
∗a, float ∗sb, float ∗wsave)

ARGUMENTS

NLength of the sequence to be transformed. The method is most efficient when N is the product of
small primes. N >= 0.

RA real array of length N containing the sequence to be transformed. On exit, R is unchanged.

AZEROThe sum from i=1 to i=n of r(i)/n

xWSAVEOn 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), 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(F4.1, 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