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/MatrixBase_cwiseAbs2.cpp b/doc/snippets/MatrixBase_cwiseAbs2.cpp
new file mode 100644
index 0000000..889a2e2
--- /dev/null
+++ b/doc/snippets/MatrixBase_cwiseAbs2.cpp
@@ -0,0 +1,4 @@
+MatrixXd m(2,3);
+m << 2, -4, 6,   
+     -5, 1, 0;
+cout << m.cwiseAbs2() << endl;