title: Problems with Eigen library and c++ linker
body: <p>I try to link my c++ application against the "Eigen 2.0.15" library.
  Some details:</p>
  
  <ul>
  <li>My compiler is: gcc version 4.0.1 (Apple Inc. build 5493)</li>
  <li>My OS is: mac os 10.5</li>
  <li><p>I compile the code with g++ -I/opt/local/include -I/opt/local/include/eigen2  -O2 -g ...</p>
  
  <p><code>Building target: LBRALL
  Invoking: MacOS X C++ Linker
  g++ -L/opt/local/lib -o "LBRALL"  [... *.o -files ]   -lcv -lEigen2 -lcxcore -lhighgui</code></p></li>
  </ul>
  
  <p>The error is:</p>
  
  <pre><code>`Undefined symbols:
  "Eigen::MatrixBase&lt;Eigen::Block&lt;Eigen::Matrix&lt;float, 4, 4, 2, 4, 4&gt;, 3, 3, 1, 32&gt;    &gt;::inverse() const", referenced from:
    Eigen::Transform&lt;float, 3&gt;::inverse(Eigen::TransformTraits) constin LBRSendStateCart.o
    Eigen::Transform&lt;float, 3&gt;::inverse(Eigen::TransformTraits) constin LBRCam.o
  "Eigen::MatrixBase&lt;Eigen::Matrix&lt;float, 4, 4, 2, 4, 4&gt; &gt;::inverse() const", referenced from:
    Eigen::Transform&lt;float, 3&gt;::inverse(Eigen::TransformTraits) constin LBRSendStateCart.o
    Eigen::Transform&lt;float, 3&gt;::inverse(Eigen::TransformTraits) constin LBRCam.o
  ld: symbol(s) not found
  collect2: ld returned 1 exit status
  make: *** [LBRALL] Error 1`
  </code></pre>
  
  <p>Does anybody have an idea why the linker fails?</p>