+++ /dev/null
-*DECK RFFTF1
- SUBROUTINE RFFTF1 (N, C, CH, WA, IFAC)
-C***BEGIN PROLOGUE RFFTF1
-C***PURPOSE Compute the forward transform of a real, periodic sequence.
-C***LIBRARY SLATEC (FFTPACK)
-C***CATEGORY J1A1
-C***TYPE SINGLE PRECISION (RFFTF1-S, CFFTF1-C)
-C***KEYWORDS FFTPACK, FOURIER TRANSFORM
-C***AUTHOR Swarztrauber, P. N., (NCAR)
-C***DESCRIPTION
-C
-C Subroutine RFFTF1 computes the Fourier coefficients of a real
-C periodic sequence (Fourier analysis). The transform is defined
-C below at output parameter C.
-C
-C The arrays WA and IFAC which are used by subroutine RFFTB1 must be
-C initialized by calling subroutine RFFTI1.
-C
-C Input Arguments
-C
-C N the length of the array R to be transformed. The method
-C is most efficient when N is a product of small primes.
-C N may change so long as different work arrays are provided.
-C
-C C a real array of length N which contains the sequence
-C to be transformed.
-C
-C CH a real work array of length at least N.
-C
-C WA a real work array which must be dimensioned at least N.
-C
-C IFAC an integer work array which must be dimensioned at least 15.
-C
-C The WA and IFAC arrays must be initialized by calling
-C subroutine RFFTI1, and different WA and IFAC arrays must be
-C used for each different value of N. This initialization
-C does not have to be repeated so long as N remains unchanged.
-C Thus subsequent transforms can be obtained faster than the
-C first. The same WA and IFAC arrays can be used by RFFTF1
-C and RFFTB1.
-C
-C Output Argument
-C
-C C C(1) = the sum from I=1 to I=N of R(I)
-C
-C If N is even set L = N/2; if N is odd set L = (N+1)/2
-C
-C then for K = 2,...,L
-C
-C C(2*K-2) = the sum from I = 1 to I = N of
-C
-C C(I)*COS((K-1)*(I-1)*2*PI/N)
-C
-C C(2*K-1) = the sum from I = 1 to I = N of
-C
-C -C(I)*SIN((K-1)*(I-1)*2*PI/N)
-C
-C If N is even
-C
-C C(N) = the sum from I = 1 to I = N of
-C
-C (-1)**(I-1)*C(I)
-C
-C Notes: This transform is unnormalized since a call of RFFTF1
-C followed by a call of RFFTB1 will multiply the input
-C sequence by N.
-C
-C WA and IFAC contain initialization calculations which must
-C not be destroyed between calls of subroutine RFFTF1 or
-C RFFTB1.
-C
-C***REFERENCES P. N. Swarztrauber, Vectorizing the FFTs, in Parallel
-C Computations (G. Rodrigue, ed.), Academic Press,
-C 1982, pp. 51-83.
-C***ROUTINES CALLED RADF2, RADF3, RADF4, RADF5, RADFG
-C***REVISION HISTORY (YYMMDD)
-C 790601 DATE WRITTEN
-C 830401 Modified to use SLATEC library source file format.
-C 860115 Modified by Ron Boisvert to adhere to Fortran 77 by
-C changing dummy array size declarations (1) to (*).
-C 881128 Modified by Dick Valent to meet prologue standards.
-C 891214 Prologue converted to Version 4.0 format. (BAB)
-C 900131 Routine changed from subsidiary to user-callable. (WRB)
-C 920501 Reformatted the REFERENCES section. (WRB)
-C***END PROLOGUE RFFTF1
- DIMENSION CH(*), C(*), WA(*), IFAC(*)
-C***FIRST EXECUTABLE STATEMENT RFFTF1
- NF = IFAC(2)
- NA = 1
- L2 = N
- IW = N
- DO 111 K1=1,NF
- KH = NF-K1
- IP = IFAC(KH+3)
- L1 = L2/IP
- IDO = N/L2
- IDL1 = IDO*L1
- IW = IW-(IP-1)*IDO
- NA = 1-NA
- IF (IP .NE. 4) GO TO 102
- IX2 = IW+IDO
- IX3 = IX2+IDO
- IF (NA .NE. 0) GO TO 101
- CALL RADF4 (IDO,L1,C,CH,WA(IW),WA(IX2),WA(IX3))
- GO TO 110
- 101 CALL RADF4 (IDO,L1,CH,C,WA(IW),WA(IX2),WA(IX3))
- GO TO 110
- 102 IF (IP .NE. 2) GO TO 104
- IF (NA .NE. 0) GO TO 103
- CALL RADF2 (IDO,L1,C,CH,WA(IW))
- GO TO 110
- 103 CALL RADF2 (IDO,L1,CH,C,WA(IW))
- GO TO 110
- 104 IF (IP .NE. 3) GO TO 106
- IX2 = IW+IDO
- IF (NA .NE. 0) GO TO 105
- CALL RADF3 (IDO,L1,C,CH,WA(IW),WA(IX2))
- GO TO 110
- 105 CALL RADF3 (IDO,L1,CH,C,WA(IW),WA(IX2))
- GO TO 110
- 106 IF (IP .NE. 5) GO TO 108
- IX2 = IW+IDO
- IX3 = IX2+IDO
- IX4 = IX3+IDO
- IF (NA .NE. 0) GO TO 107
- CALL RADF5 (IDO,L1,C,CH,WA(IW),WA(IX2),WA(IX3),WA(IX4))
- GO TO 110
- 107 CALL RADF5 (IDO,L1,CH,C,WA(IW),WA(IX2),WA(IX3),WA(IX4))
- GO TO 110
- 108 IF (IDO .EQ. 1) NA = 1-NA
- IF (NA .NE. 0) GO TO 109
- CALL RADFG (IDO,IP,L1,IDL1,C,C,C,CH,CH,WA(IW))
- NA = 1
- GO TO 110
- 109 CALL RADFG (IDO,IP,L1,IDL1,CH,CH,CH,C,C,WA(IW))
- NA = 0
- 110 L2 = L1
- 111 CONTINUE
- IF (NA .EQ. 1) RETURN
- DO 112 I=1,N
- C(I) = CH(I)
- 112 CONTINUE
- RETURN
- END