new ENABLE_SYSTEM_CONTRIB cmake option to enable use of system versions of...

new ENABLE_SYSTEM_CONTRIB cmake option to enable use of system versions of dependencies (currently Eigen)

CMakeLists.txt

@@ -131,6 +131,7 @@ if(HAVE_O3)
 endif()
 
 opt(MPI "Enable MPI" OFF)
+opt(SYSTEM_CONTRIB "Use system versions of contrib libraries, when possible" OFF)
 
 #----------------------------------
 #
@@ -143,7 +144,6 @@ add_subdirectory(src/domain)
 add_subdirectory(src/field)
 add_subdirectory(src/problem)
 include_directories(src/common src/domain src/field src/problem)
-include_directories(contrib/eigen)
 
 add_subdirectory(examples)
 add_subdirectory(tutorials)
@@ -154,6 +154,17 @@ add_subdirectory(tutorials)
 #
 #----------------------------------
 
+if(ENABLE_SYSTEM_CONTRIB)
+  find_path(EIGEN_INC "Eigen/Dense" HINTS eigen3)
+  if(EIGEN_INC)
+    include_directories(${EIGEN_INC})
+  else()
+    message(FATAL_ERROR "Could not find system Eigen - set ENABLE_SYSTEM_CONTRIB to false to use bundled version")
+  endif()
+else()
+  include_directories(contrib/eigen)
+endif()
+
 # Gmsh (Mandatory)
 
 find_library(GMSH_LIB gmsh)