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/snippets/Vectorwise_reverse.cpp b/doc/snippets/Vectorwise_reverse.cpp
new file mode 100644
index 0000000..2f6a350
--- /dev/null
+++ b/doc/snippets/Vectorwise_reverse.cpp
@@ -0,0 +1,10 @@
+MatrixXi m = MatrixXi::Random(3,4);
+cout << "Here is the matrix m:" << endl << m << endl;
+cout << "Here is the rowwise reverse of m:" << endl << m.rowwise().reverse() << endl;
+cout << "Here is the colwise reverse of m:" << endl << m.colwise().reverse() << endl;
+
+cout << "Here is the coefficient (1,0) in the rowise reverse of m:" << endl
+<< m.rowwise().reverse()(1,0) << endl;
+cout << "Let us overwrite this coefficient with the value 4." << endl;
+//m.colwise().reverse()(1,0) = 4;
+cout << "Now the matrix m is:" << endl << m << endl;