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dcffti.f
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1989-08-14
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subroutine dcffti (n,wsave)
c
c Double precision version. -tk
c
C***BEGIN PROLOGUE CFFTI
C***REVISION DATE 811015 (YYMMDD)
C***CATEGORY NO. D6
C***KEYWORDS FFT,FAST FOURIER TRANSFORM,FOURIER TRANSFORM,COMPLEX
C***DATE WRITTEN FEBRUARY 1978
C***AUTHOR SWARZTRAUBER P.N. (NCAR)
C***PURPOSE
C INITIALIZE FOR CFFTF AND CFFTB
C***DESCRIPTION
C *****************************************************************
C
C SUBROUTINE CFFTI(N,WSAVE)
C
C *****************************************************************
C
C SUBROUTINE CFFTI INITIALIZES THE ARRAY WSAVE WHICH IS USED IN
C BOTH CFFTF AND CFFTB. THE PRIME FACTORIZATION OF N TOGETHER WITH
C A TABULATION OF THE TRIGONOMETRIC FUNCTIONS ARE COMPUTED AND
C STORED IN WSAVE.
C
C INPUT PARAMETER
C
C N THE LENGTH OF THE SEQUENCE TO BE TRANSFORMED
C
C OUTPUT PARAMETER
C
C WSAVE A WORK ARRAY WHICH MUST BE DIMENSIONED AT LEAST 4*N+15
C THE SAME WORK ARRAY CAN BE USED FOR BOTH CFFTF AND CFFTB
C AS LONG AS N REMAINS UNCHANGED. DIFFERENT WSAVE ARRAYS
C ARE REQUIRED FOR DIFFERENT VALUES OF N. THE CONTENTS OF
C WSAVE MUST NOT BE CHANGED BETWEEN CALLS OF CFFTF OR CFFTB
C
C***REFERENCES
C***ROUTINES CALLED CFFTI1
C***END PROLOGUE CFFTI
implicit double precision (a-h,o-z)
dimension wsave(1)
C***FIRST EXECUTABLE STATEMENT CFFTI
if (n .eq. 1) return
iw1 = n+n+1
iw2 = iw1+n+n
call dcffti1 (n,wsave(iw1),wsave(iw2))
return
end