undefined reference poblem

[yanmengting117]

../lib/libORB_SLAM2.so: undefined reference to YAML::detail::node_data::mark_defined()' ../lib/libORB_SLAM2.so: undefined reference to YAML::convert::decode(YAML::Node const&, bool&)'
../lib/libORB_SLAM2.so: undefined reference to YAML::detail::node_data::insert_map_pair(YAML::detail::node&, YAML::detail::node&)' ../lib/libORB_SLAM2.so: undefined reference to YAML::detail::memory::create_node()'
../lib/libORB_SLAM2.so: undefined reference to YAML::detail::node_data::begin()' ../lib/libORB_SLAM2.so: undefined reference to YAML::detail::node_data::set_null()'
../lib/libORB_SLAM2.so: undefined reference to YAML::detail::node_data::end()' ../lib/libORB_SLAM2.so: undefined reference to YAML::detail::node_data::set_scalar(std::__cxx11::basic_string<char, std::char_traits, std::allocator > const&)'
../lib/libORB_SLAM2.so: undefined reference to YAML::detail::memory_holder::merge(YAML::detail::memory_holder&)' ../lib/libORB_SLAM2.so: undefined reference to YAML::detail::node_data::convert_to_map(boost::shared_ptrYAML::detail::memory_holder)'
../lib/libORB_SLAM2.so: undefined reference to `YAML::LoadFile(std::__cxx11::basic_string<char, std::char_traits, std::allocator > const&)'
collect2: error: ld returned 1 exit status
CMakeFiles/mono_tum.dir/build.make:166: recipe for target '../Examples/Monocular/mono_tum' failed
make[2]: *** [../Examples/Monocular/mono_tum] Error 1
CMakeFiles/Makefile2:141: recipe for target 'CMakeFiles/mono_tum.dir/all' failed
make[1]: *** [CMakeFiles/mono_tum.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2
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