Squashed 'third_party/eigen/' changes from 61d72f6..cf794d3


Change-Id: I9b814151b01f49af6337a8605d0c42a3a1ed4c72
git-subtree-dir: third_party/eigen
git-subtree-split: cf794d3b741a6278df169e58461f8529f43bce5d
diff --git a/doc/snippets/MatrixBase_cwiseSign.cpp b/doc/snippets/MatrixBase_cwiseSign.cpp
new file mode 100644
index 0000000..efd7179
--- /dev/null
+++ b/doc/snippets/MatrixBase_cwiseSign.cpp
@@ -0,0 +1,4 @@
+MatrixXd m(2,3);
+m <<  2, -4, 6,
+     -5,  1, 0;
+cout << m.cwiseSign() << endl;