title: undefined reference to `gsl_vector_free'
body: <p>I'm Trying to compile some c++ files using g++ , the problem that these files depends on both libxml2 and gsl libraries , whene i give the compilation command<br>
  <code>g++ -Wall -I/usr/include/libxml2  -lgsl main.cpp YUNucNet.cpp src/*.cpp -lxml2  -lm</code></p>
  
  <p>it alaways give me many linking error of undefined reference for gsl</p>
  
  <pre><code>'/tmp/ccCJrl0t.o: In function `WnSparseSolve__Phi__solve:
  WnSparseSolve.cpp:(.text+0x24bc): undefined reference to `gsl_vector_calloc'
  WnSparseSolve.cpp:(.text+0x24cc): undefined reference to `gsl_vector_calloc'
  WnSparseSolve.cpp:(.text+0x24e9): undefined reference to `gsl_vector_calloc'
  WnSparseSolve.cpp:(.text+0x24ff): undefined reference to `gsl_vector_alloc'
  WnSparseSolve.cpp:(.text+0x250f): undefined reference to `gsl_vector_calloc
  ....etc
  </code></pre>
  
  <p>what is the problem here ??</p>