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Nonequispaced fast Fourier transform
FAQ

NFFT Frequently Asked Questions with Answers

This is the list of Frequently Asked Questions about NFFT.

Using NFFT

  • Number of irregular samples (nodes), number of regular samples (frequencies)
    The cut-off frequency (length of the regular grid) is N, i.e. the total number of regular samples is the product of N[0],...,N[d-1]. The number of irregular samples (nodes) is M.

Known Issues

  • Internal compiler error when compiling fastsum
    Due to a bug in GCC versions 7.1.0 and 7.2.0, compilation of the NFFT might abort with an internal compiler error in the fastsum module. A simple workaround is disabling the applications (configure option --disable-applications).
  • Wrong NFFT calculation when enabling the debug mode or overriding the compiler flags (CFLAGS)
    Due to a bug in GCC versions 4.5.0, 4.5.1, 4.5.2, 4.5.3, 4.6.0 and 4.6.1, compiling the NFFT without the compiler flag "-ffast-math" may lead to incorrect computation results and buffer overflows.
    By default, this flag is set by the "configure" script.
    If you enable the debug mode (configure switch "--enable-debug") or set the CFLAGS manually, please add the compiler flag "-ffast-math" to the CFLAGS environment variable.
  • Internal compiler error when compiling with MRI support
    Due to a bug in GCC version 4.7.1, compilation of the NFFT with MRI module enabled (configure option --enable-mri or --enable-all) will abort with an internal compiler error.
    This problem does not occur in earlier or later versions of the GCC. A workaround was added in nfft-3.2.3.
  • Compilation fails when MRI module enabled and NNFFT module disabled
    When the NFFT is compiled with MRI and without NNFFT support, a compilation error eccurs in applications/mri/mri2d.
    Please also enable the NNFFT module when building with MRI support (configure options --enable-nnfft --enable-mri), or build all modules (--enable-all).

NFFT for Windows

We offer compiled binaries of the NFFT library and Matlab interface for 64-bit Windows on our download page. If you want to compile NFFT by yourself, you can use the following manual which should work with NFFT 3.3.2 on a 64-bit Windows PC with 64-bit Matlab.

  1. Download and install MSYS2.
  2. Start the MinGW-w64 Win64 Shell, and type the following to update your installation and install the MinGW-w64 toolchain and FFTW
    pacman -Syuu
    pacman -S mingw-w64-x86_64-toolchain make mingw-w64-x86_64-fftw
    
  3. Download and unpack the NFFT source code from the download page to your MSYS2 home directory (e.g. C:\msys64\home\JaneDoe\nfft-3.3.2, replace JaneDoe by your username).
  4. Open the NFFT directory in the MinGW shell
    cd nfft-3.3.2
    
  5. Run the configure script
    ./configure --enable-all --enable-openmp --with-matlab=/c/Programme/MATLAB/R2015b
    
    Here are some useful optional flags: --enable-all says that all modules should be compiled, --enable-openmp enables the multicore support, and --with-matlab contains the path to your Matlab installation. For a list of all available options, you can run ./configure --help.
    Note: You might run into trouble if the path of your Matlab installation contains a space (e.g. C:\Program Files). An easy way to overcome this is creating a link to your Matlab directory.
  6. Compile the nfft by running
    make
    
  7. The compiled programs need the proper libraries to run correctly, i.e., they require libfftw3-3.dll, libwinpthread-1.dll, libgcc_s_seh-1.dll, libgomp-1.dll (all in the folder mingw64/bin, the latter two are only required if openmp is enabled in the configure script). For some executebles, you might also need the .dll file from the directory nfft-3.3.2/.libs. The easiest way to add these libraries is to copy them all in the same directory you run the executeble from. Alternatively, you can put the dll files in a directory added to the Windows %PATH% environment variable (see also How do I set or change the PATH system variable?). When having problems with dependecies, check out the Dependecy Walker.
    Note: When running Matlab, the dll files should be in your current Matlab directory, adding it the Matlab path might be insufficient.