add tutorial page 1 - the Matrix class

+ 3 examples

doc/examples/tut_matrix_resize_fixed_size.cpp

@@ -0,0 +1,12 @@
+#include <iostream>
+#include <Eigen/Dense>
+
+using namespace Eigen;
+
+int main()
+{
+  Matrix4d m;
+  m.resize(4,4); // no operation
+  std::cout << "The matrix m is of size "
+            << m.rows() << "x" << m.cols() << std::endl;
+}