The code iondenofphi calculates the velocity stability of a slow electron hole. It should compile and link by "make". The code is run by ./iondenofphi and terse help is given when using the switch -h. The figures of the associated journal article are generated by the script slowpaper.sh and can be regenerated by . slowpaper.sh No warranty for any use is given or implied. Copyright (C) I H Hutchinson 2021.