significantly extend the tutorial of sparse matrices

doc/special_examples/CMakeLists.txt

@@ -0,0 +1,20 @@
+
+if(NOT EIGEN_TEST_NOQT)
+  find_package(Qt4)
+  if(QT4_FOUND)
+    include(${QT_USE_FILE})
+  endif()
+endif(NOT EIGEN_TEST_NOQT)
+
+
+if(QT4_FOUND)
+  add_executable(Tutorial_sparse_example Tutorial_sparse_example.cpp Tutorial_sparse_example_details.cpp)
+  target_link_libraries(Tutorial_sparse_example ${EIGEN_STANDARD_LIBRARIES_TO_LINK_TO} ${QT_QTCORE_LIBRARY} ${QT_QTGUI_LIBRARY})
+
+  add_custom_command(
+      TARGET Tutorial_sparse_example
+      POST_BUILD
+      COMMAND Tutorial_sparse_example
+      ARGS ${CMAKE_CURRENT_BINARY_DIR}/../html/Tutorial_sparse_example.jpeg
+  )
+endif(QT4_FOUND)