Error in gazebo in ROS Melodic

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Hi Everyone,

I am following a tutorial for gazebo in http://wiki.ros.org/simulator_gazebo/... and http://wiki.ros.org/simulator_gazebo/...

I am using ros melodic, and my ubuntu version is 17.10

My problem is: when I type in

sudo apt-get install ros-melodic-simulator-gazebo

it shows: Reading package lists... Done Building dependency tree
Reading state information... Done E: Unable to locate package ros-melodic-simulator-gazebo

But if I type in

sudo apt-get install ros-melodic-simulators

Seemingly it works out, but there is a Note says that the second line of code works for indogo version.

Moreover, I cannot use

roslaunch gazebo_worlds empty_world.launch

to launch gazebo, and it would give me like this: RLException: [empty_world.launch] is neither a launch file in package [gazebo_worlds] nor is [gazebo_worlds] a launch file name The traceback for the exception was written to the log file

I can only use

roslaunch gazebo_ros empty_world.launch

instead. It directly causes the biggest problem: When I launch gazebo, and try to follow the guide for Simple Box URDF as I type in

rosrun gazebo spawn_model -file pwd/object.urdf -urdf -z 1 -model my_object

It says [rospack] Error: package 'gazebo' not found

Can someone help me out? Great thanks in advance!