Find package Eigen3 for CMake - cmake

Question

CMake cannot find my Eigen3 package. I set an environment variable called
EIGEN3_INCLUDE_DIR
pointing to the path where FindEigen3.cmake is.
Then in the CMakelists.txt I wrote:
find_package( Eigen3 REQUIRED )
include_directories( EIGEN3_INCLUDE_DIR )
I get next message of error:
CMake Error at C:/Program Files (x86)/CMake 2.8/share/cmake-2.8/Modules/FindPackageHandleStandardArgs.cmake:91 (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):
C:/Program Files (x86)/CMake 2.8/share/cmake-2.8/Modules/FindPackageHandleStandardArgs.cmake:252 (_FPHSA_FAILURE_MESSAGE)
C:/Program Files (x86)/CMake 2.8/share/cmake-2.8/Modules/FindEigen3.cmake:76 (find_package_handle_standard_args)
test/test_quaternion/CMakeLists.txt:25 (find_package)
Any idea on what I am missing or doing wrong?

Answer 1

Since Eigen3 is completely header only, all you ever need is the path to the include directory. And this one, you are already defining manually anyway. So there is no real need for a FindEigen3.cmake or FIND_PACKAGE call.
Simply use
INCLUDE_DIRECTORIES ( "$ENV{EIGEN3_INCLUDE_DIR}" )
or
SET( EIGEN3_INCLUDE_DIR "$ENV{EIGEN3_INCLUDE_DIR}" )
IF( NOT EIGEN3_INCLUDE_DIR )
MESSAGE( FATAL_ERROR "Please point the environment variable EIGEN3_INCLUDE_DIR to the include directory of your Eigen3 installation.")
ENDIF()
INCLUDE_DIRECTORIES ( "${EIGEN3_INCLUDE_DIR}" )
A few notes:
If you want to access the content of a CMake variable, make sure to use ${...}
$ENV{....} accesses environment variables.
The second example will stop with an error if the environment variable is not set (and, thus, EIGEN3_INCLUDE_DIR cmake variable is empty)
Be careful to use quotation marks around (evaluated) variables if they could contain whitespace. Otherwise, CMake will interpret it as a list.
If you want to use custom find modules, make sure to either place them in you CMake installation or, as #Fraser pointed out above, make sure to point CMAKE_MODULE_PATH to the directory where it is. Not sure, but it could be that CMake checks the current directory as well automatically (where your CMakeLists.txt resides. Anyhow, setting EIGEN3_INCLUDE_DIR is totally unrelated to the location of FindEigen3.cmake
However, it could be that your FindEigen3 script evaluates this variable to determine the location of your Eigen3 installation.
Alternatively, self-built CMake-based projects often provide a <PackageName>Config.cmake. If you point a variable called <PackageName>_DIR to the directory containing this file, you can use FIND_PACKAGE( <PackageName> ...) as normal. See documentation of FIND_PACKAGE for details.

Answer 2

Eigen >= 3.3 has direct CMake integration, so it seems yours isn't set up correctly.
Assume Eigen has been installed to /opt/eigen/3.3 with default settings. Append or prepend the the location /opt/eigen/3.3 to the environment variable CMAKE_PREFIX_PATH e.g in bash:
export CMAKE_PREFIX_PATH="$CMAKE_PREFIX_PATH:/opt/eigen/3.3"
Then CMake should pick it up.
If you are writing your own CMakeLists.txt that uses Eigen I suggest using code like this:
find_package (Eigen3 3.3 REQUIRED)
add_executable (example example.cpp)
target_link_libraries (example Eigen3::Eigen)
You should not use include_directories since CMake 3 was released -- the targets approach should be preferred whenever available.

Answer 3

First, make sure Eigen is properly installed. Refer to the INSTALL file that comes with the tarball.
Second, copy the cmake/FindEigen3.cmake file from the tarball to the directory containing your CMakeLists.txt.
In your CMakeLists.txt add:
set(CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR})
find_package(Eigen3 REQUIRED)
include_directories(${EIGEN3_INCLUDE_DIR})
Now you should be able to do e.g. #include <Eigen/Core>.
All of this comes (mostly) from this source.
This approach has the advantage over e.g. include_directories("$ENV{EIGEN3_INCLUDE_DIR}") that it the uses CMake's standard mechanism for finding external dependencies, making it easier for someone else (or your future self) to pick up the project, possibly on another platform.
(However, it would be nice if Eigen itself installed an EigenConfig.cmake file, making it accessible through the find_package mechanism without any extra paths.)

Answer 4

I found another solution here (which referred to here) which uses the pkg-config file :
find_package(PkgConfig)
pkg_search_module(Eigen3 REQUIRED eigen3)

Answer 5

As a detailed explanation of the note 7 from the top answer of Johannes. By using the "Config mode" rather than "Module mode" of CMake find_packate(), only writing
find_package( Eigen3 REQUIRED )
include_directories( EIGEN3_INCLUDE_DIR )
in CMakeLists.txt is enough.
Please refer to the INSTALL guidance text file contained in the eigen source code directory (eg. extracted from eigen-3.3.7.tar.gz downloaded from official website), which said:
Method 2. Installing using CMake
********************************
Let's call this directory 'source_dir' (where this INSTALL file is).
Before starting, create another directory which we will call 'build_dir'.
Do:
cd build_dir
cmake source_dir
make install
The "make install" step may require administrator privileges.
You can adjust the installation destination (the "prefix")
by passing the -DCMAKE_INSTALL_PREFIX=myprefix option to cmake, as is
explained in the message that cmake prints at the end.
Just like installing usual CMake projects to your machine.
The difference from directly including the /usr/include/eigne3 or /usr/local/include/eigen3 directory is that, a configuration directory called eigen3/cmake will also be installed to /usr/share or usr/local/share. This configuration directory contains the Eigen3Config.cmake file, which can automatically be found by CMake to locate the eigen3 directory.

Answer 6

If you have not added Eigen Library to environment variable then do the following in CMakeLists.txt:
cmake_minimum_required(VERSION 3.9)
project(ProjectName)
set(CMAKE_CXX_STANDARD 11)
# set EIGEN_DIR variable to Eigen Library Path
set(EIGEN_DIR "C:\\Eigendir\\Eigen")
# include the directory
include_directories(${EIGEN_DIR})
add_executable(ProjectName main.cpp)
target_link_libraries(ProjectName ${EIGEN_DIR})

Answer 7

Another simple way that doesn't require adding an environment variable is to simply find eigen with the cmake find_path function https://cmake.org/cmake/help/v3.6/command/find_path.html. The example code finds the directory "Eigen" in paths "/usr/include/" and "/usr/local/include" with an additional search in subdirectory "eigen3".
find_path(EIGEN3_INCLUDE_DIRS "Eigen" paths "/usr/include" "/usr/local/include" path_suffixes "eigen3")
message(${EIGEN3_INCLUDE_DIRS})
if ( NOT EIGEN3_INCLUDE_DIRS )
message(FATAL_ERROR "CMake variable EIGEN3_INCLUDE_DIRS not found.")
endif()
include_directories ( "${EIGEN3_INCLUDE_DIRS}" )

Answer 8

You could try setting the CMAKE_MODULE_PATH to the location of Eigen subdirectory named "cmake":
cmake . -DCMAKE_MODULE_PATH=<Eigen root dir>/cmake/

Answer 9

I had a similar problem when run cmake .. && make on Google Colab on a project clone from github. I fixed it by editing CMakeLists.txt file and adding this line to it:
set(EIGEN3_INCLUDE_DIR "/usr/include/eigen3")
As you can see, my eigen3 was in /usr/include/eigen3 path (and I had installed it using !sudo apt-get install build-essential cmake libeigen3-dev)

Answer 10

When installing on Kubuntu 20.04 following steps from INSTALL:
Do:
cd build_dir
cmake source_dir
make install
using -DCMAKE_INSTALL_PREFIX=/usr/local/eigen-3.4.0 and sudo
FindEigen3.cmake is not installed. However, using
set(Eigen3_DIR "/usr/local/eigen/share/eigen3/cmake")
seem to work. FindEigen3.cmake is in the build directory
but it is not copied to the installation directory tree.

Answer 11

This worked:
Changed c++11 to c++14
Changed find_package(Eigen3 QUIET) to find_package(Eigen3 CONFIG)

Answer 12

Another simple way is:
if the Eigen library is in /opt/eigen/3.3/Eigen
include_directories(/opt/eigen/3.3)
which is equivalent to what Jai suggested
set(EIGEN_DIR "/opt/eigen/3.3")
include_directories(${EIGEN_DIR})

Answer 13

You need to read official documentation:
Click here
After install Eigen from tar and compile it correctly.
CMakeLists.txt will looks like this:
find_package(Eigen3 3.3 REQUIRED NO_MODULE)
add_executable(${PROJECT_NAME} something.cpp)
target_link_libraries(${PROJECT_NAME} Eigen3::Eigen)
It will be fine work.