Using Eigen libraries in ROS

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Hi, I am fairly new to ROS and was wanting to do some matrix multiplication in a node. I found that Eigen has a good range of different matrices and vectors to use but was not quite sure what modifications I would have to make to allow it to be used in ROS.

First of all when I download the libraries, where do I put them? Is it inside the workspace folder, the src folder inside the workspace folder or is it inside the package inside the src folder? So one of these:

/workspace
/workspace/src
/workspace/src/package

In addition what changes do I have to make to the CMakeLists.txt file inside the package to include these new libraries?

Is there anything else I have to do in order to get these libraries working? I take it I need to include the header files in the node files I’m using (i.e. #include <Eigen/Eigen> #include <Eigen/Eigenvalues>)

Any help would be greatly appreciated. I am using catkin and the OS is Ubuntu Kinetic 16.04. If any more information is required please don't hesitate to ask.