FSINI
Computes parameters needed by FSINT.
Required Arguments
N — Length of the sequence to be transformed. N must be greater than 1. (Input)
WFSIN — Array of length INT(2.5 * N + 15) containing parameters needed by FSINT. (Output)
FORTRAN 90 Interface
Generic: CALL FSINI (N, WFSIN)
Specific: The specific interface names are S_FSINI and D_FSINI.
FORTRAN 77 Interface
Single: CALL FSINI (N, WFSIN)
Double: The double precision name is DFSINI.
Description
The routine FSINI initializes the routine FSINT. An efficient way to make multiple calls for the same N to IMSL routine FSINT, is to use routine FSINI for initialization. (In this case, replace FSINT with F2INT.) The routine FSINI is based on the routine SINTI in FFTPACK. The package FFTPACK was developed by Paul Swarztrauber at the National Center for Atmospheric Research.
Comments
Different WFSIN arrays are needed for different values of N.
Example
In this example, we compute three distinct sine FFTs by calling FSINI once and then calling F2INT three times.
USE FSINI_INT
USE UMACH_INT
USE CONST_INT
USE F2INT_INT
IMPLICIT NONE
INTEGER N
PARAMETER (N=7)
!
INTEGER I, K, NOUT
REAL COEF(N+1), FLOAT, PI, SIN, WFSIN(32), SEQ(N)
INTRINSIC FLOAT, SIN
! Get output unit number
CALL UMACH (2, NOUT)
! Initialize the work vector WFSIN
CALL FSINI (N, WFSIN)
! Different frequencies of the same
! wave will be transformed
DO 20 K=1, 3
! Fill the data vector SEQ
! with a pure sine wave
PI = CONST('PI')
DO 10 I=1, N
SEQ(I) = SIN(FLOAT(K*I)*PI/FLOAT(N+1))
10 CONTINUE
! Compute the transform of SEQ
CALL F2INT (N, SEQ, COEF, WFSIN)
! Print results
WRITE (NOUT,99998)
WRITE (NOUT,99999) (I, SEQ(I), COEF(I), I=1,N)
20 CONTINUE
99998 FORMAT (/, 9X, 'INDEX', 6X, 'SEQ', 7X, 'COEF')
99999 FORMAT (1X, I11, 5X, F6.2, 5X, F6.2)
END
Output
INDEX SEQ COEF
1 0.38 8.00
2 0.71 0.00
3 0.92 0.00
4 1.00 0.00
5 0.92 0.00
6 0.71 0.00
7 0.38 0.00
INDEX SEQ COEF
1 0.71 0.00
2 1.00 8.00
3 0.71 0.00
4 0.00 0.00
5 -0.71 0.00
6 -1.00 0.00
7 -0.71 0.00
INDEX SEQ COEF
1 0.92 0.00
2 0.71 0.00
3 -0.38 8.00
4 -1.00 0.00
5 -0.38 0.00
6 0.71 0.00
7 0.92 0.00
