add tutorial page 1 - the Matrix class

+ 3 examples

doc/examples/tut_matrix_coefficient_accessors.cpp

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+#include <iostream>
+#include <Eigen/Dense>
+
+using namespace Eigen;
+
+int main()
+{
+  MatrixXd m(2,2);
+  m(0,0) = 3;
+  m(1,0) = 2.5;
+  m(0,1) = -1;
+  m(1,1) = m(1,0) + m(0,1);
+  std::cout << "Here is the matrix m:\n" << m << std::endl;
+  VectorXd v(2);
+  v(0) = 4;
+  v(1) = v(0) - 1;
+  std::cout << "Here is the vector v:\n" << v << std::endl;
+
+}

doc/examples/tut_matrix_resize.cpp

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+#include <iostream>
+#include <Eigen/Dense>
+
+using namespace Eigen;
+
+int main()
+{
+  MatrixXd m(2,5);
+  m.resize(4,3);
+  std::cout << "The matrix m is of size "
+            << m.rows() << "x" << m.cols() << std::endl;
+  std::cout << "It has " << m.size() << " coefficients" << std::endl;
+  VectorXd v(2);
+  v.resize(5);
+  std::cout << "The vector v is of size " << v.size() << std::endl;
+  std::cout << "As a matrix, v is of size "
+            << v.rows() << "x" << v.cols() << std::endl;
+}

doc/examples/tut_matrix_resize_fixed_size.cpp

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+#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;
+}