Ubuntu 14.04 安装 ROS indigo 出错：ros-indigo-desktop-full:i386

出错内容：

Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:

 ros-indigo-desktop-full:i386 : 

Depends: ros-indigo-desktop:i386 but it is not going to be installed

Depends: ros-indigo-perception:i386 but it is not going to be installed

Depends: ros-indigo-simulators:i386 but it is not going to be installed

E: Unable to correct problems, you have held broken packages.

解决方法（按以下方法安装，其中第一步与其他的教程不同，第三步必须要有）：

sudo sh -c '. /etc/lsb-release && echo "deb http://mirror.umd.edu/packages.ros.org/ros/ubuntu $DISTRIB_CODENAME main" > /etc/apt/sources.list.d/ros-latest.list'
wget https://raw.githubusercontent.com/ros/rosdistro/master/ros.key -O - | sudo apt-key add -
sudo apt-get update
sudo apt-get install ros-indigo-desktop-full