make errors : cannot find -lmxnet

Hi,I build the project follow the ReadME instructions.
and errors occur as blew when I run 'make -j4':
`
make -j4
Scanning dependencies of target mtcnn
[ 11%] Building CXX object src/libmtcnn/CMakeFiles/mtcnn.dir/comm_lib.cpp.o
[ 33%] Building CXX object src/libmtcnn/CMakeFiles/mtcnn.dir/mtcnn.cpp.o
[ 33%] Building CXX object src/libmtcnn/CMakeFiles/mtcnn.dir/mxnet_mtcnn.cpp.o
[ 44%] Building CXX object src/libmtcnn/CMakeFiles/mtcnn.dir/utils.cpp.o
[ 55%] Linking CXX shared library ../../../lib/libmtcnn.so
/usr/bin/ld: cannot find -lmxnet
collect2: error: ld returned 1 exit status
src/libmtcnn/CMakeFiles/mtcnn.dir/build.make:202: recipe for target '../lib/libmtcnn.so' failed
make[2]: *** [../lib/libmtcnn.so] Error 1
CMakeFiles/Makefile2:106: recipe for target 'src/libmtcnn/CMakeFiles/mtcnn.dir/all' failed
make[1]: *** [src/libmtcnn/CMakeFiles/mtcnn.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2
`
any solution will be appreciated.