Reductions/Broadcasting/Visitor Tutorial added

doc/examples/Tutorial_ReductionsVisitorsBroadcasting_broadcast_1nn.cpp

@@ -0,0 +1,24 @@
+#include <iostream>
+#include <Eigen/Dense>
+
+using namespace std;
+using namespace Eigen;
+
+int main()
+{
+  Eigen::MatrixXf m(2,4);
+  Eigen::VectorXf v(2);
+  
+  m << 1, 23, 6, 9,
+       3, 11, 7, 2;
+       
+  v << 2,
+       3;
+
+  MatrixXf::Index index;
+  // find nearest neighbour
+  (m.colwise() - v).colwise().squaredNorm().minCoeff(&index);
+
+  cout << "Nearest neighbour is column " << index << ":" << endl;
+  cout << m.col(index) << endl;
+}