Eigen3安装、查看Eigen版本及修改FindEigen.cmake文件等一系列操作

1、安装其实很简单，由于Eigen只是用到其头文件，故安装Eigen只需把解压后文件移动至系统目录下即可：

sudo cp -r /home/bruce/software/eigen_333 /usr/local/include

以上命令把eigen3.3.3移动至/usr/local/include目录下，可以理解为安装成功。

2、如果按此方法安装了多个版本，时间一长可能会记不清某个文件夹是哪个Eigen版本，可通过如下命令进行查看：

cat /usr/local/include/eigen_333/Eigen/src/Core/util/Macros.h | grep VERSION

输出结果如下：

#define EIGEN_WORLD_VERSION 3
#define EIGEN_MAJOR_VERSION 3
#define EIGEN_MINOR_VERSION 3
#define EIGEN_VERSION_AT_LEAST(x,y,z) (EIGEN_WORLD_VERSION>x || (EIGEN_WORLD_VERSION>=x && \
                                      (EIGEN_MAJOR_VERSION>y || (EIGEN_MAJOR_VERSION>=y && \
                                                                 EIGEN_MINOR_VERSION>=z))))
#if defined(__CC_ARM) || defined(__ARMCC_VERSION)
    ((defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 199901))       \
  || (defined(_LIBCPP_VERSION) && !defined(_MSC_VER)))

这就表示是Eigen3.3.3版本。

3、在安装某些包或编译工程文件的时候会遇到一个问题，比如，即使在CMakeLists.txt文件里添加了

set(EIGEN_INCLUDE_DIR "/usr/local/include/eigen_333")、find_package(Eigen 3.3 REQUIRED)，但是仍然找不到

所需的Eigen版本，它会自动找到usr/include/eigen3文件夹下，这就需要修改工程包含的FindEigen.cmake

文件了，作如下修改即可（根据自己的文件夹而定）：

  if (EIGEN3_FOUND)
    set(FOUND_INSTALLED_EIGEN_CMAKE_CONFIGURATION TRUE)
    set(EIGEN_FOUND ${EIGEN3_FOUND})
    set(EIGEN_INCLUDE_DIR "/usr/local/include/eigen_333" CACHE STRING
      "Eigen include directory" FORCE)
  else()

一般情况下，就能成功解决，若不成功，尝试把文件中类似的全部改。

有些时候.cmake文件会不一样，但是修改方法大同小异：

macro(EIGEN_REPORT_NOT_FOUND REASON_MSG)
  unset(EIGEN_FOUND)
  unset(EIGEN_INCLUDE_DIRS)
  # Make results of search visible in the CMake GUI if Eigen has not
  # been found so that user does not have to toggle to advanced view.
  mark_as_advanced(CLEAR EIGEN_INCLUDE_DIR)
  # Note _FIND_[REQUIRED/QUIETLY] variables defined by FindPackage()
  # use the camelcase library name, not uppercase.
  if (Eigen_FIND_QUIETLY)
    message(STATUS "Failed to find Eigen - " ${REASON_MSG} ${ARGN})
  elseif (Eigen_FIND_REQUIRED)
    message(FATAL_ERROR "Failed to find Eigen - " ${REASON_MSG} ${ARGN})
  else()
    # Neither QUIETLY nor REQUIRED, use no priority which emits a message
    # but continues configuration and allows generation.
    message("-- Failed to find Eigen - " ${REASON_MSG} ${ARGN})
  endif ()
  return()
endmacro(EIGEN_REPORT_NOT_FOUND)

# Protect against any alternative find_package scripts for this library having
# been called previously (in a client project) which set EIGEN_FOUND, but not
# the other variables we require / set here which could cause the search logic
# here to fail.
unset(EIGEN_FOUND)

# Search user-installed locations first, so that we prefer user installs
# to system installs where both exist.
list(APPEND EIGEN_CHECK_INCLUDE_DIRS
  /usr/local/include
  /usr/local/homebrew/include # Mac OS X
  /opt/local/var/macports/software # Mac OS X.
  /opt/local/include
  /usr/include
  /usr/local/include/eigen_333)
# Additional suffixes to try appending to each search path.
list(APPEND EIGEN_CHECK_PATH_SUFFIXES
  eigen3 # Default root directory for Eigen.
  Eigen/include/eigen3 # Windows (for C:/Program Files prefix) < 3.3
  Eigen3/include/eigen3 
  Eigen) # Windows (for C:/Program Files prefix) >= 3.3

# Search supplied hint directories first if supplied.
find_path(EIGEN_INCLUDE_DIR
  NAMES Eigen/Core
  #PATHS ${EIGEN_INCLUDE_DIR_HINTS}
  PATHS $"/usr/local/include/eigen_333"
  ${EIGEN_CHECK_INCLUDE_DIRS}
  PATH_SUFFIXES ${EIGEN_CHECK_PATH_SUFFIXES})

if (NOT EIGEN_INCLUDE_DIR OR
    NOT EXISTS ${EIGEN_INCLUDE_DIR})
  eigen_report_not_found(
    "Could not find eigen3 include directory, set EIGEN_INCLUDE_DIR to "
    "path to eigen3 include directory, e.g. /usr/local/include/eigen_333")
endif (NOT EIGEN_INCLUDE_DIR OR
       NOT EXISTS ${EIGEN_INCLUDE_DIR})

# Mark internally as found, then verify. EIGEN_REPORT_NOT_FOUND() unsets
# if called.
set(EIGEN_FOUND TRUE)

# Extract Eigen version from Eigen/src/Core/util/Macros.h
if (EIGEN_INCLUDE_DIR)
  set(EIGEN_VERSION_FILE /usr/local/include/eigen_333/Eigen/src/Core/util/Macros.h)
  if (NOT EXISTS ${EIGEN_VERSION_FILE})
    eigen_report_not_found(
      "Could not find file: ${EIGEN_VERSION_FILE} "
      "containing version information in Eigen install located at: "
      "${EIGEN_INCLUDE_DIR}.")
  else (NOT EXISTS ${EIGEN_VERSION_FILE})
    file(READ ${EIGEN_VERSION_FILE} EIGEN_VERSION_FILE_CONTENTS)

    string(REGEX MATCH "#define EIGEN_WORLD_VERSION [0-9]+"
      EIGEN_WORLD_VERSION "${EIGEN_VERSION_FILE_CONTENTS}")
    string(REGEX REPLACE "#define EIGEN_WORLD_VERSION ([0-9]+)" "\\1"
      EIGEN_WORLD_VERSION "${EIGEN_WORLD_VERSION}")

    string(REGEX MATCH "#define EIGEN_MAJOR_VERSION [0-9]+"
      EIGEN_MAJOR_VERSION "${EIGEN_VERSION_FILE_CONTENTS}")
    string(REGEX REPLACE "#define EIGEN_MAJOR_VERSION ([0-9]+)" "\\1"
      EIGEN_MAJOR_VERSION "${EIGEN_MAJOR_VERSION}")

    string(REGEX MATCH "#define EIGEN_MINOR_VERSION [0-9]+"
      EIGEN_MINOR_VERSION "${EIGEN_VERSION_FILE_CONTENTS}")
    string(REGEX REPLACE "#define EIGEN_MINOR_VERSION ([0-9]+)" "\\1"
      EIGEN_MINOR_VERSION "${EIGEN_MINOR_VERSION}")

    # This is on a single line s/t CMake does not interpret it as a list of
    # elements and insert ';' separators which would result in 3.;2.;0 nonsense.
    set(EIGEN_VERSION "${EIGEN_WORLD_VERSION}.${EIGEN_MAJOR_VERSION}.${EIGEN_MINOR_VERSION}")
  endif (NOT EXISTS ${EIGEN_VERSION_FILE})
endif (EIGEN_INCLUDE_DIR)

# Set standard CMake FindPackage variables if found.
if (EIGEN_FOUND)
  set(EIGEN_INCLUDE_DIRS ${EIGEN_INCLUDE_DIR})
endif (EIGEN_FOUND)

# Handle REQUIRED / QUIET optional arguments and version.
include(FindPackageHandleStandardArgs)
find_package_handle_standard_args(Eigen
  REQUIRED_VARS EIGEN_INCLUDE_DIRS
  VERSION_VAR EIGEN_VERSION)

# Only mark internal variables as advanced if we found Eigen, otherwise
# leave it visible in the standard GUI for the user to set manually.
if (EIGEN_FOUND)
  mark_as_advanced(FORCE EIGEN_INCLUDE_DIR)
endif (EIGEN_FOUND)