Compiling code include Eigen library needs permission

I just copy the Eigen folder to /usr/local/include according to this post, to use Eigen library.

Now to compile a simple example it needs to compile with sudo:

simple1.cpp:2:23: fatal error: /usr/local/include/Eigen/Dense: Permission denied 

What's wrong? I think it should not ask for permission. Can I fix it?

Edit

I also changed the permission of folder to drwxr-xr-x and added

export LD_LIBRARY_PATH="/usr/local/include/Eigen/" 

and log out once. Still, I need permission to compile.

namei -lx /usr/local/include/Eigen/Dense f: /usr/local/include/Eigen/Dense Drwxr-xr-x root root / drwxr-xr-x root root usr drwxr-xr-x root root local drwxr-xr-x root root include drwxr-xr-x root root Eigen -rw-r--r-- root root Dense 

Know someone who can answer? Share a link to this question via email, Twitter, or Facebook.