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66 lines
2.3 KiB
Fortran
66 lines
2.3 KiB
Fortran
*DECK COSTI
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SUBROUTINE COSTI (N, WSAVE)
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C***BEGIN PROLOGUE COSTI
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C***PURPOSE Initialize a work array for COST.
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C***LIBRARY SLATEC (FFTPACK)
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C***CATEGORY J1A3
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C***TYPE SINGLE PRECISION (COSTI-S)
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C***KEYWORDS COSINE FOURIER TRANSFORM, FFTPACK
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C***AUTHOR Swarztrauber, P. N., (NCAR)
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C***DESCRIPTION
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C
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C Subroutine COSTI initializes the array WSAVE which is used in
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C subroutine COST. The prime factorization of N together with
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C a tabulation of the trigonometric functions are computed and
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C stored in WSAVE.
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C
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C Input Parameter
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C
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C N the length of the sequence to be transformed. The method
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C is most efficient when N-1 is a product of small primes.
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C
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C Output Parameter
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C
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C WSAVE a work array which must be dimensioned at least 3*N+15.
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C Different WSAVE arrays are required for different values
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C of N. The contents of WSAVE must not be changed between
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C calls of COST.
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C
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C***REFERENCES P. N. Swarztrauber, Vectorizing the FFTs, in Parallel
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C Computations (G. Rodrigue, ed.), Academic Press,
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C 1982, pp. 51-83.
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C***ROUTINES CALLED RFFTI
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C***REVISION HISTORY (YYMMDD)
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C 790601 DATE WRITTEN
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C 830401 Modified to use SLATEC library source file format.
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C 860115 Modified by Ron Boisvert to adhere to Fortran 77 by
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C (a) changing dummy array size declarations (1) to (*),
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C (b) changing references to intrinsic function FLOAT
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C to REAL, and
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C (c) changing definition of variable PI by using
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C FORTRAN intrinsic function ATAN instead of a DATA
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C statement.
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C 881128 Modified by Dick Valent to meet prologue standards.
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C 890531 Changed all specific intrinsics to generic. (WRB)
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C 890531 REVISION DATE from Version 3.2
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C 891214 Prologue converted to Version 4.0 format. (BAB)
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C 920501 Reformatted the REFERENCES section. (WRB)
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C***END PROLOGUE COSTI
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DIMENSION WSAVE(*)
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C***FIRST EXECUTABLE STATEMENT COSTI
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IF (N .LE. 3) RETURN
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PI = 4.*ATAN(1.)
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NM1 = N-1
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NP1 = N+1
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NS2 = N/2
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DT = PI/NM1
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FK = 0.
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DO 101 K=2,NS2
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KC = NP1-K
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FK = FK+1.
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WSAVE(K) = 2.*SIN(FK*DT)
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WSAVE(KC) = 2.*COS(FK*DT)
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101 CONTINUE
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CALL RFFTI (NM1,WSAVE(N+1))
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RETURN
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END
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