ngspice supports the battle-tested fftw library for fast and accurate FFT calculation. The fedora package of ngspice doesn't include fftw-devel as a BuildRequires, so the built-in and rather limited FFT routines are used (a).

Since fftw is already packaged and readily available on fedora, and is a widely used and mature library, it would be lovely if the fedora package went ahead and depended on it.

the autotools configure script should detect its availability without any changed, but you could also use --with-fftw3=yes to force it.

(a) among other things, the built in fft is limited to power-of-2 length inputs, which means zero-padding and thus an unforseen shift in the location of frequency bins in the results. It's also potentially slower than the optimized fftw library.

Reproducible: Always