Cfft2b Cfft2f Cfft2i Rfft2b Rfft2c Rfft2f Rfft2i

Rfft2c() Sub Rfft2c ( L As  Long, M As  Long, R() As  Double, C() As  Complex, Info As  Long  ) Full complex data of two-dimensional Fourier transform obtained by Rfft2f Purpose This routine reconstructs the full complex data from the packed two-dimensional Fourier transform obtained by Rfft2f. Refer to the description of Rfft2f for the details of packed form. Parameters [in] L Number of elements to be transformed in the first dimension of the two-dimensional array R(). (L >= 1) [in] M Number of elements to be transformed in the second dimension of the two-dimensional array R(). (M >= 1) [in,out] R() Array R(LR1 - 1, LR2 - 1) (LR1 >= L, LR2 >= M) Two dimensional Fourier forward transform data in packed form obtained by Rfft2f. [in] C() Array C(LC1 - 1, LC2 - 1) (LC1 >= L, LC2 >= M) The full complex data reconstructed from the packed two-dimensional Fourier transform in R(). [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 R() is invalid. (Array R() is not big enough) = -5: The argument C() is invalid. (Array C() is not big enough) Example Program Compute the two-dimensional Fourier transform of 4 rows x 4 columns random data sequence by Rfft2f. Reconstruct the full complex data from the obtained packed data by Rfft2c. Then compute the backward transform by Cfft2b and compare with the original data sequence. Sub Ex_Rfft2c() Const L = 4, M = 4 Dim Wsave() As Double, R(L - 1, M - 1) As Double, R0(L - 1, M - 1) As Double Dim C(L - 1, M - 1) As Complex Dim LWsave As Long, Info As Long, I As Long, J As Long '-- Initialization LWsave = L + 3 * M + Log(L) / Log(2) + 2 * Log(M) / Log(2) + 12 ReDim Wsave(LWsave - 1) Call Rfft2i(L, M, Wsave, Info) If Info <> 0 Then GoTo Err '-- Generate test data For I = 0 To L - 1 For J = 0 To M - 1 R(I, J) = Rnd() R0(I, J) = R(I, J) Next Next '-- Forward transform Call Rfft2f(L, M, R(), Wsave(), Info) If Info <> 0 Then GoTo Err '-- Convert to full complex data Call Rfft2c(L, M, R(), C(), Info) '-- Initialization for Cfft2b LWsave = 2 * (L + M) + Log(L) / Log(2) + Log(M) / Log(2) + 8 ReDim Wsave(LWsave - 1) Call Cfft2i(L, M, Wsave, Info) If Info <> 0 Then GoTo Err '-- Backward transform by Cfft2b Call Cfft2b(L, M, C(), Wsave(), Info) If Info <> 0 Then GoTo Err '-- Print result For J = 0 To M - 1 For I = 0 To L - 1 Debug.Print R0(I, J), Creal(C(I, J)), Cimag(C(I, J)), Creal(C(I, J)) - R0(I, J) Next Debug.Print Next Exit Sub Err: Debug.Print "Error in Rfft2i/Rfft2f/Rfft2b: Info =", Info End Sub Example Results 0.902888596057892 0.902888596057892 0 0 0.449173510074615 0.449173510074615 0 0 0.91016560792923 0.91016560792923 0 0 0.415564596652985 0.415564596652985 0 0 0.419061899185181 0.419061899185181 0 0 0.52361536026001 0.52361536026001 0 0 0.356703519821167 0.356703519821167 0 0 0.341727256774902 0.341727256774902 0 0 0.614621579647064 0.614621579647064 0 0 0.320736587047577 0.320736587047577 0 0 0.423278748989105 0.423278748989105 0 0 0.214545428752899 0.214545428752899 0 0 0.733203768730164 0.733203768730164 0 0 0.805532574653625 0.805532574653625 0 0 0.942486166954041 0.942486166954041 0 0 0.579672455787659 0.579672455787659 0 0