fftw

Using FFTW I have been computing the FFT of normalized .wav file data. I am a bit confused as to how I should normalise the FFT output, however. I have been using the method which seemed obvious to me, which is simply to divide by the highest FFT magnitude. I have seen division by 1/N and N/2 recommended, however (where I assume N = FFT size). How do these work as normalisation factors? There doesn't seem to me to be an intuitive relation between these factors and the actual data - so what am I missing? Huge thanks in advance for any help on this. Surprisingly there is no single agreed

The FFTW manual says that its fftw_complex type is bit compatible to std::complex<double> class in STL. But that doesn't work for me: #include <complex> #include <fftw3.h> int main() { std::complex<double> x(1,0); fftw_complex fx; fx = reinterpret_cast<fftw_complex>(x); } This gives me an error: error: invalid cast from type ‘std::complex<double>’ to type ‘double [2]’ What am I doing wrong? Re-write your code as follows: #include <complex> #include <fftw3.h> int main() { std::complex<double> x(1,0); fftw_complex fx; memcpy( &fx, &x, sizeof( fftw_complex ) ); } Every compiler I've used will

I am currently working on a project where I need to implement a fourier transform and an inverse transform. I was testing a program I modified from an online example; the print or write commands are normally for debugging purposes: program testit INCLUDE 'fftw3.f' double complex out!, in real in parameter (N=100) dimension in(N), out(N) integer*8 p,p2 integer i,j real x real fact write(*,*)"stuff in data" OPEN(UNIT=12, FILE="input.txt", ACTION="write", STATUS="replace") OPEN(UNIT=20, FILE="dftoutput.txt", ACTION="write", STATUS="replace") x=0 in = 0 do i=1,N/2 in(i)=1 enddo do i=1,N write(*,"

Consider a 2D transform of the form L x M (column major setup), from a complex array src to a real array tgt . Or , in Fortranese, complex(C_DOUBLE_COMPLEX), pointer :: src(:,:) real(8), pointer :: tgt(:,:) . Corresponding pointers are type(C_PTR) :: csrc,ctgt . I would allocate them in the following manner: ! The complex array first alloc_local = fftw_mpi_local_size_2d(M,L/2+1,MPI_COMM_WORLD,local_M,local_offset1) csrc = fftw_alloc_complex(alloc_local) call c_f_pointer(csrc, src, [L/2,local_M]) ! Now the real array alloc_local = fftw_mpi_local_size_2d(2*(L/2+1),M, & MPI_COMM_WORLD,local_L

I am trying to install the fftw3 package through R console >install.packages("fftw") After this command it is asking to select the cran mirror.I have selected the cran mirror then following error occurs: Loading Tcl/Tk interface ... done Warning: unable to access index for repository http://ftp.iitm.ac.in/cran/src/contrib Warning messages: 1: In open.connection(con, "r") : unable to connect to 'cran.r-project.org' on port 80. 2: In getDependencies(pkgs, dependencies, available, lib) : package ‘fftw’ is not available (for R version 2.14.1) And When I am trying for fftw3 then following error

I have a 2D array of data stored in column-major (Fortran-style) format, and I'd like to take the FFT of each row . I would like to avoid transposing the array (it is not square). For example, my array fftw_complex* data = new fftw_complex[21*256]; contains entries [r0_val0, r1_val0,..., r20_val0, r0_val1,...,r20_val255] . I can use fftw_plan_many_dft to make a plan to solve each of the 21 FFTs in-place in the data array if it is row -major, e.g. [r0_val0, r0_val1,..., r0_val255, r1_val0,...,r20_val255] : int main() { int N = 256; int howmany = 21; fftw_complex* data = new fftw_complex[N

I'm using Windows 10 and Visual Studio 2015. In C++, I need to get the Fourier-transform of an image for applying filters on it. It seems that FFTW++ is the ideal solution for this, however I can't get it to compile, and its driving me mad. I'm relatively new to programming so I don't know how embarrassing this is. I used the NuGet function in Visual Studio to get the FFTW library. Since I couldn't find it on NuGet I downloaded the FFTW+ stuff from the following link: https://sourceforge.net/projects/fftwpp/ I copied the content of the download to the project folder, and included the header