title: Eigen compilation error with MPI
body: <p>I am trying to do domain decomposition using Zoltan library and want to implement Eigen.
  Unfortunately, the moment I include Eigen in the header <code>#include &lt;Eigen/Dense&gt;</code>, I get the following compilation error:</p>
  
  <p>SRC/init_system.cpp:24:23: fatal error: Eigen/Dense: No such file or directory
   #include 
                         ^
  compilation terminated.</p>
  
  <p>Even, I have included the Eigen path in the makefile, as shown below:</p>
  
  <pre><code>CXX=mpic++
  
  ID_TYPE_FLAG=-DZOLTAN_ID_TYPE_LONG_LONG
  
  BLD=/home/kumar/Software/Zoltan/Zoltan_v3.83/BuildDir/src
  
  SRC=/home/kumar/Software/Zoltan/Zoltan_v3.83/src
  
  ZOLTAN_INCLUDE=-I$(SRC)/include
  
  ZOLTAN_CONFIG_INCLUDE=-I$(BLD)/include
  
  ZOLTAN_UTIL_INCLUDE=-I$(SRC)/zz  \
                      -I$(SRC)/par \
                      -I$(SRC)/order \
                      -I$(SRC)/tpls \
                      -I$(SRC)/lb \
                      -I$(SRC)/params \
                      -I$(SRC)/Utilities/shared
  
  
  CXXFLAGS  = -Wall -g3 -std=c++11 -I include/eigen3 -$(ID_TYPE_FLAG)
  
  COPT    = -DMKL_ILP64 -m64
  
  LIBS    = -lmkl_intel_ilp64 -lmkl_core -lmkl_intel_thread -liomp5 -lpthread -lm -ldl -lmkl_core -lmkl_intel_thread -lzoltan -lparmetis -lmetis -lptscotch -lscotch -lptscotcherr -lscotcherr
  
  CXXFLAGS =$(ID_TYPE_FLAG)
  
  ODIR    = /OBJ
  CFILES  := $(wildcard SRC/*.cpp)
  OFILES  := $(addprefix OBJ/,$(notdir $(CFILES:.cpp=.o)))
  
  meshl:  $(OFILES)
      $(CXX) $(CXXFLAGS) -o $@ $(OFILES) $(LIBS)
  OBJ/%.o: SRC/%.cpp
      $(CXX) $(CXXFLAGS) -c $(COPT) $&lt; -o $@
  
  clean:
      rm -f OBJ/*.o
  </code></pre>
  
  <p>The domain decompositoin code using Zoltan is compiling absolutely fine with mpi when the header for Eigen is NOT included in the code.</p>
  
  <p>Any help in this regard for implementing Eigen would be appreciated.</p>
  
  <p>Thank you for your time !!</p>