Use the included Eigen by default, but allow to override EIGEN3_INCLUDE_DIR

CMakeLists.txt

@@ -50,7 +50,11 @@ endif()
 find_package(Boost 1.50.0 COMPONENTS system REQUIRED)
 message(STATUS "Boost found at ${Boost_INCLUDE_DIRS}")
 
-set(CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake)
+set(CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/3rdparty/eigen/cmake)
+# Use the Eigen included in the submodule by default, but allow the user to override EIGEN3_INCLUDE_DIR:
+if(NOT DEFINED EIGEN3_INCLUDE_DIR)
+  set(EIGEN3_INCLUDE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/3rdparty/eigen)
+endif()
 find_package(Eigen3 REQUIRED)
 message(STATUS "Eigen3 found: ${EIGEN3_FOUND}, version: ${EIGEN3_VERSION}")
 message(STATUS "Eigen3 include dir found at ${EIGEN3_INCLUDE_DIR}")