big improvements to tutorial, especially page 2 (matrix arithmetic).

add placeholders for some 'special topic' pages.

doc/examples/tut_arithmetic_matrix_mul.cpp

@@ -0,0 +1,19 @@
+#include <iostream>
+#include <Eigen/Dense>
+
+using namespace Eigen;
+int main()
+{
+  Matrix2d mat;
+  mat << 1, 2,
+         3, 4;
+  Vector2d vec(-1,1);
+  RowVector2d rowvec(2,0);
+  std::cout << "Here is mat*mat:\n" << mat*mat << std::endl;
+  std::cout << "Here is mat*vec:\n" << mat*vec << std::endl;
+  std::cout << "Here is rowvec*mat:\n" << rowvec*mat << std::endl;
+  std::cout << "Here is rowvec*vec:\n" << rowvec*vec << std::endl;
+  std::cout << "Here is vec*rowvec:\n" << vec*rowvec << std::endl;
+  std::cout << "Let's multiply mat by itself" << std::endl;
+  std::cout << "Now mat is mat:\n" << mat << std::endl;
+}