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/examples/make_circulant.cpp.entry b/doc/examples/make_circulant.cpp.entry
new file mode 100644
index 0000000..f9d2eb8
--- /dev/null
+++ b/doc/examples/make_circulant.cpp.entry
@@ -0,0 +1,5 @@
+template <class ArgType>
+Circulant<ArgType> makeCirculant(const Eigen::MatrixBase<ArgType>& arg)
+{
+  return Circulant<ArgType>(arg.derived());
+}