pr2_nav_tutorial.launch is not a launch file name.

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i run the "PR2 Simulator Workshop" and in section 8.PR2 Navigation Stack Demo I create a launch script for starting all necessary navigation components, and save it as ~/pr2_nav_tutorial.launch in my home directory (user@ubuntu). When i run: roslaunch ~/pr2_nav_tutorial.launch I take: /home/user/pr2_nav_tutorial.launch] is not a launch file name. Also, i have not the pr2_nav_tutorial package.