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rfft1i

  1. C RFFT1I    SOURCE    BP208322  18/10/08    21:15:18     9952           
  2. CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
  3. C
  4. C   FFTPACK 5.1 
  5. C
  6. C   Authors:  Paul N. Swarztrauber and Richard A. Valent
  7. c 
  8. c  FFTPACK 5.1 routine RFFT2I initializes real array WSAVE for use 
  9. c  in its companion routines RFFT2F and RFFT2B for computing the two-
  10. c  dimensional fast Fourier transform of real data.  Prime 
  11. c  factorizations of L and M, together with tabulations of the 
  12. c  trigonometric functions, are computed and stored in array WSAVE.
  13. c  RFFT2I must be called prior to the first call to RFFT2F or RFFT2B.
  14. c  Separate WSAVE arrays are required for different values of L or M.
  15. c  
  16. c  Input Arguments
  17. c  
  18. c  L       Integer number of elements to be transformed in the first 
  19. c          dimension.  The transform is most efficient when L is a 
  20. c          product of small primes.
  21. c  
  22. c  M       Integer number of elements to be transformed in the second 
  23. c          dimension.  The transform is most efficient when M is a 
  24. c          product of small primes.
  25. c  
  26. c  LENSAV  Integer number of elements in the WSAVE array.  LENSAV must
  27. c          be at least L + 3*M + INT(LOG(REAL(L))/LOG(2.)) +
  28. c          2*INT(LOG(REAL(M))/LOG(2.)) +12.
  29. c 
  30. c 
  31. c  Output Arguments
  32. c  
  33. c  WSAVE   Real work array with dimension LENSAV, containing the
  34. c          prime factors of L and M, and also containing certain 
  35. c          trigonometric values which will be used in routines 
  36. c          RFFT2B or RFFT2F.
  37. c 
  38. c 
  39. c  IER     Integer error return
  40. c          =  0 successful exit
  41. c          =  2 input parameter LENSAV not big enough
  42. c          = 20 input error returned by lower level routine
  43. C
  44. CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
  45.  
  46.       SUBROUTINE RFFT1I ( N, WSAVE, LENSAV, IER )
  47.       IMPLICIT INTEGER(I-N)
  48.       IMPLICIT REAL*8(A-H,O-Z)
  49.       INTEGER    N, LENSAV, IER
  50.       REAL*8     WSAVE(LENSAV)
  51. C
  52.       IER = 0
  53. C
  54.       IF (LENSAV .LT. N + INT(LOG(REAL(N))/LOG(2.)) +4) THEN
  55.         IER = 2
  56. c         CALL XERFFT ('RFFT1I ', 3)
  57.         call erreur(5)
  58.         return
  59.       ENDIF
  60. C
  61.       IF (N .EQ. 1) RETURN
  62. C
  63.       CALL RFFTI1 (N,WSAVE(1),WSAVE(N+1))
  64.       RETURN
  65.       END
  66.  
  67.  
  68.  

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