Install gri-pdf-doc by entering the following commands in the terminal:
sudo apt update sudo apt install gri-pdf-doc
Description:
PostScript manual for gri, a language for scientific graphics
Gri is a command-driven application for making x-y graphs, contour-graphs, and image graphs. . This is the Gri manual in PDF format suitable for printing or viewing on-screen. The compressed file is located at /usr/share/doc/gri/gri.pdf.gz
Homepage: http://gri.sourceforge.net/
Version: 2.12.26-1build1
Section: universe/doc