1. error building g2o_with_orbslam2: ‘MatrixExponential’ is not a member of ‘Eigen’
install another version of eigen will solve this problem.
http://eigen.tuxfamily.org/index.php?title=News:Eigen_3.2.10_released!sudo updatedb
locate eigen3 sudo rm -rf /usr/include/eigen3 /usr/lib/cmake/eigen3 /usr/share/doc/libeigen3-dev /usr/share/pkgconfig/eigen3.pc /var/lib/dpkg/info/libeigen3-dev.list /var/lib/dpkg/info/libeigen3-dev.md5sums
sudo updatedb
locate eigen3 从eigen官网，下载3.1.0版本，
http://eigen.tuxfamily.org/index.php?title=Special%3AAllPages&from=&to=&namespace=100
得到一个压缩包eigen-eigen-bf4cb8c934fa.tar.bz2，提取，在文件夹内执行
https://blog.csdn.net/ganbaoni9yang/article/details/83956999
https://blog.csdn.net/j_____j/article/details/80622570
http://eigen.tuxfamily.org/index.php?title=Main_Page
https://blog.csdn.net/sunshinefcx/article/details/84137856
http://eigen.tuxfamily.org/dox-3.2/unsupported/MatrixExponential_8h_source.html
How to check the version number of Eigen C++ template library?
pkg-config --modversion eigen3