add examples for makeJacobi and makeGivens

doc/snippets/Jacobi_makeGivens.cpp

@@ -0,0 +1,6 @@
+Vector2f v = Vector2f::Random();
+PlanarRotation<float> G;
+G.makeGivens(v.x(), v.y());
+cout << "Here is the vector v:" << endl << v << endl;
+v.applyOnTheLeft(0, 1, G.adjoint());
+cout << "Here is the vector J' * v:" << endl << v << endl;

doc/snippets/Jacobi_makeJacobi.cpp

@@ -0,0 +1,8 @@
+Matrix2f m = Matrix2f::Random();
+m = (m + m.adjoint()).eval();
+PlanarRotation<float> J;
+J.makeJacobi(m, 0, 1);
+cout << "Here is the matrix m:" << endl << m << endl;
+m.applyOnTheLeft(0, 1, J.adjoint());
+m.applyOnTheRight(0, 1, J);
+cout << "Here is the matrix J' * m * J:" << endl << m << endl;

doc/snippets/compile_snippet.cpp.in

@@ -4,6 +4,7 @@
 #include <Eigen/QR>
 #include <Eigen/Cholesky>
 #include <Eigen/Geometry>
+#include <Eigen/Jacobi>
 
 using namespace Eigen;
 using namespace std;