Error: /usr/bin/ld: cannot find -lfl

Error: /usr/bin/ld: cannot find -lfl
collect2: error: ld returned 1 exit status
Makefile:69: recipe for target 'unified' failed
make: *** [unified] Error 1

Solution: sudo apt-get install flex

How to install libsndfile and Armadillo library on ubuntu

Installation of libsndfile:

sudo apt-get install libsndfile-dev

Installation of Armadillo

1.  If not present already, install LAPACK, Boost and BLAS  with 

   sudo apt-get install liblapack-dev  sudo apt-get install libblas-dev  sudo apt-get install libboost-dev

2. Install Armadillo using 

   sudo apt-get install libarmadillo-dev