Cfft2b Cfft2f Cfft2i Rfft2b Rfft2c Rfft2f Rfft2i

Rfft2i() Sub Rfft2i ( L As  Long, M As  Long, Wsave() As  Double, Info As  Long  ) Initialization of work data for Rfft2f and Rfft2b Purpose This routine initializes array Wsave() for use in its companion routines Rfft2f and Rfft2b. The prime factorization of L and M together with a tabulation of the trigonometric functions are computed and stored in array Wsave(). Note - The initialization of Wsave() is not necessary for the succeeding call of Rfft2f or Rfft2b for the same L and M values. If the value of L or M has been changed, Wsave() should be re-initialized by this routine. Parameters [in] L Number of elements to be transformed in the first dimension of the two-dimensional array C(). (L >= 1) (The transform is most efficient when L is a product of small primes) [in] M Number of elements to be transformed in the second dimension of the two-dimensional array C(). (M >= 1) (The transform is most efficient when M is a product of small primes) [in] Wsave() Array Wsave(LWsave - 1) (LWsave >= L + 3*M + ln(L)/ln(2) + 2*ln(M)/ln(2) + 12) Work data. Its contents must be initialized with a call to Rfft2i before the first call to Rfft2f or Rfft2b for a given transform length L and M. [out] Info = 0: Successful exit. = -1: The argument L had an illegal value. (L < 1) = -2: The argument M had an illegal value. (M < 1) = -3: The argument Wsave() is invalid. (Array Wsave() is not big enough) Reference FFTPACK Example Program See example of Rfft2f.