It seems that it is not a very good idea to install nvidia drivers from ppa, as it is not maintained by nvidia:
bob@desktop:~/isaac$ sudo add-apt-repository ppa:graphics-drivers/ppa
bob@desktop:~/isaac$ sudo apt-get update
bob@desktop:~/isaac$ sudo apt-get install nvidia-driver-418
It seems that it should rather be a cuda installation with a driver using official nvidia distribution system, that is maintained by nvidia, rather than installation of drivers from a third party repository that is not maintained by nvidia, in my opinion.