$ sudo apt-get update
$ sudo apt-get install ptex-jtex 

ptex-jtex is installed in your system.

Make ensure the ptex-jtex package were installed using the commands given below,

$ sudo dpkg-query -l | grep ptex-jtex *

You will get with ptex-jtex package name, version, architecture and description in a table

ptex-jtex package basic information: