Squashed 'third_party/eigen/' content from commit 61d72f6

Change-Id: Iccc90fa0b55ab44037f018046d2fcffd90d9d025
git-subtree-dir: third_party/eigen
git-subtree-split: 61d72f6383cfa842868c53e30e087b0258177257
diff --git a/doc/examples/DenseBase_template_int_middleCols.cpp b/doc/examples/DenseBase_template_int_middleCols.cpp
new file mode 100644
index 0000000..6191d79
--- /dev/null
+++ b/doc/examples/DenseBase_template_int_middleCols.cpp
@@ -0,0 +1,15 @@
+#include <Eigen/Core>
+#include <iostream>
+
+using namespace Eigen;
+using namespace std;
+
+int main(void)
+{
+    int const N = 5;
+    MatrixXi A(N,N);
+    A.setRandom();
+    cout << "A =\n" << A << '\n' << endl;
+    cout << "A(:,1..3) =\n" << A.middleCols<3>(1) << endl;
+    return 0;
+}