fatal error: Eigen/Dense: No such file or directory - c++

Question

I have installed libeigen3-dev in order to compile programs using Eigen 3. when I include a file, such as Eigen/Dense I get this error when I try to run g++:
user#office-debian:~/Documents/prog$ g++ src/main.cpp -MMD -std=c++11
In file included from src/main.cpp:9:0:
src/tdefs.h:16:23: fatal error: Eigen/Dense: No such file or directory
compilation terminated.
Running the following line works fine:
g++ -I /usr/include/eigen3/ src/main.cpp -MMD -std=c++11
shouldn't that include directory be automatically found by GCC because I installed the Eigen package through aptitude? Why are boost and OpenGL found automatically when I install the libraries but not Eigen? (Note that eigen is a header-only library, but that shouldn't matter right?)
Running g++ src/main.cpp -MMD -std=c++11 --verbose produces the following output:
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.7/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.7.2-5' --with-bugurl=file:///usr/share/doc/gcc-4.7/README.Bugs --enable-languages=c,c++,go,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.7 --enable-shared --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.7 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin --enable-objc-gc --with-arch-32=i586 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.7.2 (Debian 4.7.2-5)
COLLECT_GCC_OPTIONS='-MMD' '-std=c++11' '-v' '-shared-libgcc' '-mtune=generic' '-march=x86-64'
/usr/lib/gcc/x86_64-linux-gnu/4.7/cc1plus -quiet -v -imultiarch x86_64-linux-gnu -MMD main.d -D_GNU_SOURCE src/main.cpp -quiet -dumpbase main.cpp -mtune=generic -march=x86-64 -auxbase main -std=c++11 -version -o /tmp/ccoYRPKY.s
GNU C++ (Debian 4.7.2-5) version 4.7.2 (x86_64-linux-gnu)
compiled by GNU C version 4.7.2, GMP version 5.0.5, MPFR version 3.1.0-p10, MPC version 0.9
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/include/c++/4.7
/usr/include/c++/4.7/x86_64-linux-gnu
/usr/include/c++/4.7/backward
/usr/lib/gcc/x86_64-linux-gnu/4.7/include
/usr/local/include
/usr/lib/gcc/x86_64-linux-gnu/4.7/include-fixed
/usr/include/x86_64-linux-gnu
/usr/include
End of search list.
GNU C++ (Debian 4.7.2-5) version 4.7.2 (x86_64-linux-gnu)
compiled by GNU C version 4.7.2, GMP version 5.0.5, MPFR version 3.1.0-p10, MPC version 0.9
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 66d178dd81da8c975e003e06d9f5e782
In file included from src/main.cpp:9:0:
src/tdefs.h:16:23: fatal error: Eigen/Dense: No such file or directory
compilation terminated.

Answer 1

I had this same problem on my Ubuntu 14 box. Ended up creating symlinks to get around it. With eigen3 installed in /usr/local/include do the following:
cd /usr/local/include
sudo ln -sf eigen3/Eigen Eigen
sudo ln -sf eigen3/unsupported unsupported
You should now be able to include the headers by:
#include <Eigen/Dense>
#include <unsupported/Eigen/FFT>

Answer 2

Change
#include <Eigen/Dense>
to
#include <eigen3/Eigen/Dense>

Answer 3

Run your compiler with the --verbose switch:
g++ --verbose ...
If your includes are relative to one of the paths shown in this output, you don't have to use -I. It depends how gcc has been configured, and it depends where that other stuff is installed.
Note that . is typically not in the -I paths.
Later
After exchanging a couple of comments it is clear that /usr/include/eigen3/Eigen/Dense should be include-able by #include <Eigen/Dense>, but not by #include <eigen3/Eigen/Dense>. Therefore, the addition of the command line option -I /usr/include/eigen3 is mandatory.
Whether some installation selects to install header files into a directory that in one of the ones compiled into gcc, depends on the default, a decision made by the distributor, or a decision made during installation. I'd say that "frequently used" header files (Boost) are well placed into /usr/local/include while some "elitist" stuff would be better off in a directory of its own.

Answer 4

Should use the following:
#if defined __GNUC__ || defined __APPLE__
#include <Eigen/Dense>
#else
#include <eigen3/Eigen/Dense>
#endif

Answer 5

This worked for me (using Macports for installing Shogun on Mac OS 10.11):
cd ${macports_prefix}/include
sudo ln -sf eigen3/Eigen Eigen
sudo ln -sf eigen3/unsupported unsupported

Answer 6

If you are working on a Linux server, and you have to install Eigen to a local directory, you can try to solve the problem by following the steps:
Download, install, and extract Eigen source code from the official website.
Copy the Eigen folder to a directory where your local lib is. In my case, I downloaded, unzipped and install eigen-3.4.0, and then I copied the entire folder Eigen in /eigen-3.4.0/Eigen/ to my local include /anywhere/include/Eigen.
Add this path when you run g++ -g yourcode.cpp -I /anywhere/include -L /anywhere/lib'

Answer 7

I'm using Ubuntu 22.04, with Eigen installed by
sudo apt install libeigen3-dev
according to the above method (the answer from scottlittle), I link the Eigen to /usr/include by
cd ~/usr/include
sudo ln -sf eigen3/Eigen Eigen
sudo ln -sf eigen3/unsupported unsupported
After this step, I can use
#include <Eigen/Dense>
instead of
#include <eigen3/Eigen/Dense>

Answer 8

If you follow the getting started instructions at the main Eigen site then you can't go far wrong.
To surmise, download then extract the Eigen source code into a directory of choice. Next copy the "Eigen" directory into /usr/local/include/. NOTE this is the directory named "Eigen" WITHIN the directory structure extracted, NOT the entire directory structure itself. It worked for me on an Ubuntu 14.04 virtual machine.