Eigen is a pure header library meaning everything is in the .hpp files. Eigen is implemented using the expression templates technique, which builds structures at compile time, where expressions are evaluated only as needed. This means it builds expression trees at compile time and generates custom code to evaluate them
This technique enables the programmer to bypass the normal order of expression evaluation in the C++ and achieve optimizations such as loop fusion and loop unrolling.
Installation is fairly straightforward, on debian based OS:
sudo apt-get install libeigen3-dev
or if you want to build it from source code just clone it:
git clone https://gitlab.com/libeigen/eigen.git
make the the build directory:
cd eigen
mkdir build
cd build
Now build and install it,
cmake -DCMAKE_CXX_FLAGS=-std=c++1z -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX:PATH=~/usr .. && make -j8 all install
please note that I have set:
-DCMAKE_INSTALL_PREFIX:PATH=~/usr
This way the Eigen will be installed in home/<user-name>/usr and not in the /usr so no root privilege is needed.
Now in your CMake file you have to set the Eigen3_DIR:
set(Eigen3_DIR "$ENV{HOME}/usr/share/eigen3/cmake")
find_package (Eigen3 REQUIRED NO_MODULE)
MESSAGE("EIGEN3_FOUND: " ${EIGEN3_FOUND})
MESSAGE("EIGEN3_INCLUDE_DIR: " ${EIGEN3_INCLUDE_DIR})
MESSAGE("EIGEN3_VERSION: " ${EIGEN3_VERSION})
MESSAGE("EIGEN3_VERSION_STRING: " ${EIGEN3_VERSION_STRING})
add_executable (example example.cpp)
target_link_libraries (example Eigen3::Eigen)