message: Added example 23 to CMakeLists
diff: @@ -29,6 +29,7 @@ list(APPEND ALL_EXE_SRCS
  ex20.cpp
  ex21.cpp
  ex22.cpp
  + ex23.cpp
  )
  if (MFEM_USE_MPI)
  @@ -55,6 +56,7 @@ if (MFEM_USE_MPI)
  ex20p.cpp
  ex21p.cpp
  ex22p.cpp
  + ex23p.cpp
  )
  endif()
  