dcosqi(3P)

NAME

dcosqi - initialize the array xWSAVE, which is used in both xCOSQF and xCOSQB.

SYNOPSIS

SUBROUTINE COSQI (N, RWSAVE)

SUBROUTINE DCOSQI (N, DWSAVE)

SUBROUTINE VCOSQI (N, RWSAVE)

SUBROUTINE VDCOSQI (N, DWSAVE)

#include <sunperf.h>

void costi (int n, float ∗rwsave) ;

void dcosti (int n, double ∗dwsave) ;

void vcosti (int n, float ∗rwsave) ;

void vdcosti (int n, float ∗dwsave) ;

ARGUMENTS

N Length of the sequence to be transformed. The method is most efficient when N is a product of small primes.

xWSAVE On entry, an array with a dimension of at least (3 ∗ N + 15) for scalar subroutines or (2 ∗ N + 15) for vector subroutines. The same work array can be used for both xCOSQF and xCOSQB as long as N remains unchanged. Different xWSAVE arrays are required for different values of N. This initialization does not have to be repeated between calls to xCOSQF or xCOSQB as long as N and xWSAVE remain unchanged, thus subsequent transforms can be obtained faster than the first.

SAMPLE PROGRAM

      PROGRAM TEST
      IMPLICIT NONE
C
      INTEGER       N
      PARAMETER    (N = 6)
C
      INTEGER       I
      REAL          PI, WSAVE(3 ∗ N + 15), X(N)
C
      EXTERNAL      COSQB, COSQF, COSQI
      INTRINSIC     ACOS, COS
C
C     Initialize array X to a real even quarter-wave sequence, that is,
C     it can be expanded in terms of a cosine series with only odd wave
C     numbers.
C
      PI = ACOS (-1.0)
      DO 100, I=1, N
        X(I) = COS((I - 1) ∗ PI / (2.0 ∗ N))
100 CONTINUE
C
      CALL COSQI (N, WSAVE)
      PRINT 1000
      PRINT 1010, (X(I), I = 1, N)
      CALL COSQF (N, X, WSAVE)
      PRINT 1020
      PRINT 1010, (X(I), I = 1, N)
      CALL COSQB (N, X, WSAVE)
      PRINT 1030
      PRINT 1010, (X(I), I = 1, N)
C
1000 FORMAT(1X, ’Original Sequence: ’)
1010 FORMAT(1X, 100(F7.3, 1X))
1020 FORMAT(1X, ’Transformed Sequence: ’)
1030 FORMAT(1X, ’Recovered Sequence: ’)
      END

SAMPLE OUTPUT

Original Sequence:
   1.000   0.966   0.866   0.707   0.500   0.259
Transformed Sequence:
   6.000   0.000   0.000   0.000   0.000   0.000
Recovered Sequence:
24.000 23.182 20.785 16.971 12.000   6.212