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/Tutorial_commainit_02.cpp b/doc/snippets/Tutorial_commainit_02.cpp
new file mode 100644
index 0000000..c960d6a
--- /dev/null
+++ b/doc/snippets/Tutorial_commainit_02.cpp
@@ -0,0 +1,7 @@
+int rows=5, cols=5;
+MatrixXf m(rows,cols);
+m << (Matrix3f() << 1, 2, 3, 4, 5, 6, 7, 8, 9).finished(),
+     MatrixXf::Zero(3,cols-3),
+     MatrixXf::Zero(rows-3,3),
+     MatrixXf::Identity(rows-3,cols-3);
+cout << m;