Unable to find Eigen3 with CMake

Question

I am kind of desperate: For my studies I need to work with Eigen and CMake. I'm able to use Eigen if I copy the whole library in the directories where my compiler looks by default but as soon as I try to find it via
find_package(Eigen3 REQUIRED)
I get the following error:

CMake Error at /usr/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:148 (message):
  Could NOT find Eigen3 (missing: EIGEN3_INCLUDE_DIR EIGEN3_VERSION_OK)
  (Required is at least version "2.91.0")
Call Stack (most recent call first):
  /usr/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:388 (_FPHSA_FAILURE_MESSAGE)
  FindEigen3.cmake:76 (find_package_handle_standard_args)
  CMakeLists.txt:8 (find_package)

-- Configuring incomplete, errors occurred!

Now I searched for solutions but all I those I tried (also those available on stackoverflow:
Find package Eigen3 for CMake or CMake Can't find Eigen3 ) did not work. My Eigen Version (according to the Macros in Core/util/Macros.h) is 3.2.5. I keep the Eigen directory in /usr/local/include, I use the FindEigen3.cmake which comes with the Eigen library and my CMakeLists.txt looks as follows:

cmake_minimum_required(VERSION 2.8)
project(Test)

set(CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR})
find_package(Eigen3 REQUIRED)
include_directories(${EIGEN3_INCLUDE_DIR})
message("Found Eigen3 in: ${EIGEN3_INCLUDE_DIR}")

add_executable(main test.cpp)

Has anyone an idea what's going wrong?

Kind regards, Julien

Answer 1

Turning my comment into an answer

The find package scripts - like FindEigen3.cmake - normally use the find_path() command to detect the package's include directory (see it's documentation for the full details).

FindEigen3.cmake uses the following code snippet:

find_path(EIGEN3_INCLUDE_DIR NAMES signature_of_eigen3_matrix_library
    PATHS
    ${CMAKE_INSTALL_PREFIX}/include
    ${KDE4_INCLUDE_DIR}
    PATH_SUFFIXES eigen3 eigen
)

So it looks in CMAKE_INSTALL_PREFIX which on Unix/Linux hosts is /usr/local by default.

The following has worked for me:

• Go to the Eigen source directory and run the CMake and installation steps

  > mkdir build
  > cd build
  > cmake ..
  > make install
  

• Then copy - as you have done - FindEigen3.cmake to your projects source directory.

• Now your code does find Eigen (just changed to list(APPEND ...))

  list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}")
  find_package(Eigen3 REQUIRED)
  

References

• Eigen & CMake
• CMake: Of what use is find_package() if you need to specify CMAKE_MODULE_PATH anyway?
• Cmake doesn't find Boost