title: fatal error: eigen3/Eigen/Core: No such file or directory
body: <p>I am not aware of C++ but I am trying to run this <a href="https://github.com/speedinghzl/DSRG" rel="nofollow noreferrer">project</a> which says to create a wrapper by running the command <code>pip install CRF/</code>. I am trying to do the same but I am running into this error.</p>
  
  <pre><code>    ERROR: Command errored out with exit status 1:
     command: /home/ssindhu/deeplab_env/bin/python3.6 -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-req-build-pmpk49o5/setup.py'"'"'; __file__='"'"'/tmp/pip-req-build-pmpk49o5/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' bdist_wheel -d /tmp/pip-wheel-ytpsnw2f --python-tag cp36
         cwd: /tmp/pip-req-build-pmpk49o5/
    Complete output (30 lines):
    Warning: Extension name 'krahenbuhl2013/wrapper' does not match fully qualified name 'krahenbuhl2013.wrapper' of 'krahenbuhl2013/wrapper.pyx'
    running bdist_wheel
    running build
    running build_py
    creating build
    creating build/lib.linux-x86_64-3.6
    creating build/lib.linux-x86_64-3.6/krahenbuhl2013
    copying krahenbuhl2013/__init__.py -&gt; build/lib.linux-x86_64-3.6/krahenbuhl2013
    copying krahenbuhl2013/CRF.py -&gt; build/lib.linux-x86_64-3.6/krahenbuhl2013
    running build_ext
    building 'krahenbuhl2013/wrapper' extension
    creating build/temp.linux-x86_64-3.6
    creating build/temp.linux-x86_64-3.6/krahenbuhl2013
    creating build/temp.linux-x86_64-3.6/src
    gcc -pthread -Wno-unused-result -Wsign-compare -DNDEBUG -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -D_GNU_SOURCE -fPIC -fwrapv -fPIC -I/home/ssindhu/deeplab_env/lib64/python3.6/site-packages/numpy/core/include -Iinclude -I/usr/include/eigen3 -I/usr/include/python3.6m -c krahenbuhl2013/wrapper.cpp -o build/temp.linux-x86_64-3.6/krahenbuhl2013/wrapper.o
    In file included from /home/ssindhu/deeplab_env/lib64/python3.6/site-packages/numpy/core/include/numpy/ndarraytypes.h:1830:0,
                     from /home/ssindhu/deeplab_env/lib64/python3.6/site-packages/numpy/core/include/numpy/ndarrayobject.h:12,
                     from /home/ssindhu/deeplab_env/lib64/python3.6/site-packages/numpy/core/include/numpy/arrayobject.h:4,
                     from krahenbuhl2013/wrapper.cpp:438:
    /home/ssindhu/deeplab_env/lib64/python3.6/site-packages/numpy/core/include/numpy/npy_1_7_deprecated_api.h:17:2: warning: #warning "Using deprecated NumPy API, disable it with " "#define NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION" [-Wcpp]
     #warning "Using deprecated NumPy API, disable it with " \
      ^
    In file included from krahenbuhl2013/../include/densecrf.h:29:0,
                     from krahenbuhl2013/../include/densecrf_wrapper.h:1,
                     from krahenbuhl2013/wrapper.cpp:440:
    krahenbuhl2013/../include/unary.h:28:29: fatal error: eigen3/Eigen/Core: No such file or directory
     #include &lt;eigen3/Eigen/Core&gt;
                                 ^
    compilation terminated.
    error: command 'gcc' failed with exit status 1
    ----------------------------------------
    ERROR: Failed building wheel for CRF
  </code></pre>
  
  <p>Initially it was <code>#include &lt;Eigen/Core&gt;</code> but I followed this <a href="https://github.com/opencv/opencv/issues/14868" rel="nofollow noreferrer">discussion</a> and changed it to <code>eigen3/Eigen/Core</code>. But I am getting the same error in both cases. As a person with extremely limited knowledge in c++, what should I do to resolve this error.</p>