update

1 files changed, 27 insertions, 0 deletions

diff --git a/eigen/doc/examples/class_FixedVectorBlock.cpp b/eigen/doc/examples/class_FixedVectorBlock.cpp
new file mode 100644
index 0000000..c88c9fb
--- /dev/null
+++ b/eigen/doc/examples/class_FixedVectorBlock.cpp
@@ -0,0 +1,27 @@
+#include <Eigen/Core>
+#include <iostream>
+using namespace Eigen;
+using namespace std;
+
+template<typename Derived>
+Eigen::VectorBlock<Derived, 2>
+firstTwo(MatrixBase<Derived>& v)
+{
+  return Eigen::VectorBlock<Derived, 2>(v.derived(), 0);
+}
+
+template<typename Derived>
+const Eigen::VectorBlock<const Derived, 2>
+firstTwo(const MatrixBase<Derived>& v)
+{
+  return Eigen::VectorBlock<const Derived, 2>(v.derived(), 0);
+}
+
+int main(int, char**)
+{
+  Matrix<int,1,6> v; v << 1,2,3,4,5,6;
+  cout << firstTwo(4*v) << endl; // calls the const version
+  firstTwo(v) *= 2;              // calls the non-const version
+  cout << "Now the vector v is:" << endl << v << endl;
+  return 0;
+}