unable to correct problems, you have held broken packages.

Problem “e: unable to correct problems, you have held broken packages.”

the following packages have unmet dependencies: ros-melodic-desktop-full : 
depends: ros-melodic-perception but it is not going to be installed 
depends: ros-melodic-simulators but it is not going to be installed
 e: unable to correct problems, 
 you have held broken packages.the following packages have unmet dependencies:
  ros-melodic-desktop-full : 
  depends: ros-melodic-perception but it is not going to be installed 
  depends: ros-melodic-simulators but it is not going to be installed 
  e: unable to correct problems, you have held broken packages.

Solution

sudo apt-get install aptitude
sudo aptitude install ros-melodic-desktop-full

Ref

https://answers.ros.org/question/282399/sudo-apt-get-install-ros-indigo-desktop-full-e-unable-to-correct-problems-you-have-held-broken-packages/