title: compilation error when including directory containing headers
body: <p>I have a directory <code>maths</code> which is a library that is comprised solely of header files.
  I am trying to compile my program by running the following command in my home directory:</p>
  
  <pre><code>g++ -I ../maths prog1.cpp prog2.cpp test.cpp -o et -lboost_date_time -lgsl -lgslcblas
  </code></pre>
  
  <p>but I get the following compilation error:</p>
  
  <pre><code>prog1.cpp:4:23: fatal error: maths/Dense: No such file or directory
  compilation terminated.
  prog2.cpp:6:23: fatal error: maths/Dense: No such file or directory
  compilation terminated.
  </code></pre>
  
  <p><code>maths</code> is located in the same directory(i.e. my home directory) as the .cpp files and I am running the compilation line from my home as well.</p>
  
  <p>prog1.cpp and prog2.cpp have the following headers
  <code>#include&lt;maths/Dense&gt;</code> on lines 4 and 6 respectively, hence I am getting the error.</p>
  
  <p>how do I fix it. </p>