first,I create a package with the command line

catkin_create_pkg beginner_tutorials roscpp rospy std_msgs cmd_vel_mux kobuki_saftey_controller

then write a .py file in directory of beginnertutorials/scripts. finally,I run the command line 'catkinmake',and the error ocuured. The error like this:

   ***Cmake Error at /opt/ros/groovy/share/catkin/cmake/catkinconfig.cmake 71(find_package)
   Could not find a configuration file for package cmd_vel_mux.

   Set cmd_vel_mux_DIR to the directory containing a cmake   configuration file for cmd_vel_mux.The file will have one of the following names:

   cmd_vel_muxConfig.cmake
   cmd_vel_mux-config.Cmake

call stack (most recent call first):
   beginner_tutorials/CmakeLists.text7(find package):

Cmake Error at /opt/ros/groovy/share/catkin/cmake/catkinconfig.cmake 71:(find_package)
   Could not find a configuration file for package kobuki_saftey_controller. 

  Set kobuki_saftey_controller_DIR to the directory containing a cmake   configuration file for kobuki_saftey_controller.The file will have one of the following names:

   kobuki_saftey_controllerConfig.cmake
   kobuki_saftey_controller-config.Cmake

call stack (most recent call first):

   beginner_tutorials/CmakeLists.text7(find package):***

Who can tell me why.