Some of Takin's program modules optionally require Gnuplot. It is especially recommended in order to have a live-display of the progress in the command-line version of the convolution fitter. The steps to correctly install Gnuplot and its graphical output terminals are given as follows (pick the package manager which applies for your system):
apt-get install gnuplot gnuplot-qt
dnf install gnuplot
yum install gnuplot
pacman -S gnuplot
brew install gnuplot --with-qt --with-x11