Eigen 3.4.0 installation

1. Eigen downloads the tar.gz of The latest stable release is Eigen 3.4.0.

2. Direct decompression: sudo tar -xvzf eigen-3.4.0.tar.gz

3. cmake compilation + install installation + copy the eigen file to the local calling folder /usr/include

    cd eigen-3.4.0

    sudo mkdir build

    cd build

    sudo cmake ..

    sudo make install

    sudo cp -r /usr/local/include/eigen3 /usr/include

4. Version check

pkg-config --modversion eigen3