Undefined symbols for x86_64 architecture: "cv :: face :: createFisherFaceRecognizer (int, double)" referenced by: _main in main.o

I am working on video facial recognition using opencv. I followed a tutorial on the opencv site ( http://docs.opencv.org/modules/contrib/doc/facerec/tutorial/facerec_video_recognition.html ). I am getting the following error when I try to build my code in xcode.

Undefined symbols for x86_64 architecture: "cv :: face :: createFisherFaceRecognizer (int, double)" referenced by: _main in main.o ld: symbol (s) not found for x86_64 architecture clang: error: linker command failed with exit code 1 (use -v to see the call).

I made a few changes to the code given here fatal error: file opencv2 / contrib / contrib.hpp 'not found (open cv already built)

Please read it as I am new to opencv.

Thanks in advance!