title: Eigen3 fails to install with cmake : RegexUtils not found
body: <p>I try to install eigen3.3.7 with cmake on ubuntu 16 but cmake fails. </p>
  
  <p>I follow the INSTALL file hints : 
  1) I extract the tar archive
  2) Make a "build" dir named buildDir
  3) Go to build dir : cd buildDir
  4) Start cmake : cmake ../Eigen</p>
  
  <p>Then the cmake process ends up with the error :</p>
  
  <p>CMake Error at CMakeLists.txt:1 (include):
    include could not find load file:</p>
  
  <pre><code>RegexUtils
  </code></pre>
  
  <p>CMake Error at CMakeLists.txt:2 (test_escape_string_as_regex):
    Unknown CMake command "test_escape_string_as_regex".</p>
  
  <p>May I ask you some hints please ?
  Regards
  Sylvain</p>
  
  <p>I followed the advices of chtz, but it still fails, see below the console output :</p>
  
  <pre><code>     syl@spica:~/tmp/eigen/eigen-eigen-323c052e1731$ cat INSTALL 
  Installation instructions for Eigen
  ***********************************
  Method 2. Installing using CMake
  ********************************
  
  Let's call this directory 'source_dir' (where this INSTALL file is).
  Before starting, create another directory which we will call 'build_dir'.
  
  Do:
  
    cd build_dir
    cmake source_dir
    make install
  
  syl@spica:~/tmp/eigen/eigen-eigen-323c052e1731$ mkdir build &amp;&amp; cd build
  
  syl@spica:~/tmp/eigen/eigen-eigen-323c052e1731/build$ cmake ../
  CMake Error at CMakeLists.txt:1 (include):
    include could not find load file:
  
      RegexUtils
  
  
  CMake Error at CMakeLists.txt:2 (test_escape_string_as_regex):
    Unknown CMake command "test_escape_string_as_regex".
  
  
  CMake Warning (dev) in CMakeLists.txt:
    No cmake_minimum_required command is present.  A line of code such as
  
      cmake_minimum_required(VERSION 3.5)
  
    should be added at the top of the file.  The version specified may be lower
    if you wish to support older CMake versions for this project.  For more
    information run "cmake --help-policy CMP0000".
  This warning is for project developers.  Use -Wno-dev to suppress it.
  
  -- Configuring incomplete, errors occurred!
  See also "/home/syl/tmp/eigen/eigen-eigen-323c052e1731/CMakeFiles/CMakeOutput.log".
  syl@spica:~/tmp/eigen/eigen-eigen-323c052e1731/build$ vim ../CMakeFiles/CMakeOutput.log
  </code></pre>
  
  <p>Thanks for helping.</p>