Install libfftw3-doc by entering the following commands in the terminal:
sudo apt update sudo apt install libfftw3-doc
Description:
Documentation for fftw version 3
The FFTW library computes Fast Fourier Transforms (FFT) in one or more dimensions. It is extremely fast. This package contains the documentation for the fftw3 library.
Homepage: http://fftw.org
Version: 3.3.7-1
Section: doc