dcosti(3P)

NAME

dcosti - initialize the array xWSAVE, which is used in xCOST.

SYNOPSIS

SUBROUTINE COSTI (N, RWSAVE)

SUBROUTINE DCOSTI (N, DWSAVE)

SUBROUTINE VCOSTI (N, RWSAVE)

SUBROUTINE VDCOSTI (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 - 1 is a product of small primes. N >= 2.

xWSAVE On entry, an array with a dimension of at least (3 ∗ N + 15). Different xWSAVE arrays are required for different values of N. This initialization does not have to be repeated between calls to xCOST 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 = 9)
C
      INTEGER         I
      REAL            PI, X(N), WSAVE(3 ∗ N + 15)
C
      EXTERNAL        COST, COSTI
      INTRINSIC       ACOS, COS
C
C     Initialize the array X to an even sequence, that is, it can be
C     expanded in terms of a trigonometric series that contains only
C     cosine terms.
C
      PI = ACOS (-1.0)
      DO 100, I=1, N
        X(I) = COS ((I - 1.0) ∗ 2.0 ∗ PI / (N - 1.0))
100 CONTINUE
C
      CALL COSTI (N, WSAVE)
      PRINT 1000
      PRINT 1010, (X(I), I = 1, N)
      CALL COST (N, X, WSAVE)
      PRINT 1020
      PRINT 1010, (X(I), I = 1, N)
      CALL COST (N, X, WSAVE)
      PRINT 1030
      PRINT 1010, (X(I), I = 1, N)
C
1000 FORMAT (1X, ’Original Sequence: ’)
1010 FORMAT (1X, 100(F5.1, 1X))
1020 FORMAT (1X, ’Transformed Sequence: ’)
1030 FORMAT (1X, ’Recovered Sequence: ’)
      END

SAMPLE OUTPUT

Original Sequence:
   1.0   0.7   0.0 -0.7 -1.0 -0.7   0.0   0.7   1.0
Transformed Sequence:
   0.0   0.0   8.0   0.0   0.0   0.0   0.0   0.0   0.0
Recovered Sequence:
16.0 11.3   0.0 -11.3 -16.0 -11.3   0.0 11.3 16.0