Eigen(3):error: ‘Eigen’ has not been declared

Compiling c++ When you file , Report errors ：

error: ‘Eigen’ has not been declared

Solution examples ：

CMakeLists.txt in

         Note that there are “#”

cmake_minimum_required(VERSION 2.8.3)
project(xxx)

set(CMAKE_BUILD_TYPE "Release")
set(CMAKE_CXX_FLAGS "-std=c++11")
set(CMAKE_CXX_FLAGS_RELEASE "-O3 -Wall -g")

find_package(catkin REQUIRED COMPONENTS
  geometry_msgs
  nav_msgs
  sensor_msgs
  roscpp
  rospy
  rosbag
  std_msgs
  image_transport
  cv_bridge
  tf
  pcl_conversions
)

include_directories("/usr/local/include/eigen3")#eigen3 route 
set(PCL_DIR "/usr/share/pcl-1.8")
set(OpenCV_DIR "/usr/share/OpenCV") 
find_package(Eigen3 REQUIRED)# lookup eigen3 package 
find_package(PCL REQUIRED)
find_package(OpenCV 3.2 REQUIRED)
find_package(Ceres REQUIRED)

include_directories(
  # include
	${catkin_INCLUDE_DIRS} 
	${PCL_INCLUDE_DIRS}
	${EIGEN3_INCLUDE_DIR}# take eigen3 Contents included 
  ${CERES_INCLUDE_DIRS}
  ${OpenCV_INCLUDE_DIRS})

catkin_package(
  CATKIN_DEPENDS geometry_msgs nav_msgs roscpp rospy std_msgs pcl_conversions
  DEPENDS EIGEN3 PCL # As a dependency 
  # INCLUDE_DIRS include
)

cpp In file

         Add... In the header file

#include <Eigen/Dense>

Here's the ros answer in , Propose reference header file ：

#include <eigen3/Eigen/Eigen>

#include <Eigen/Eigen>

I tried , It fails to work well （ Maybe you can try ）

Eigen libriary does not work - ROS Answers: Open Source Q&A Forum