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/ComplexSchur_matrixT.cpp b/doc/snippets/ComplexSchur_matrixT.cpp
new file mode 100644
index 0000000..8380571
--- /dev/null
+++ b/doc/snippets/ComplexSchur_matrixT.cpp
@@ -0,0 +1,4 @@
+MatrixXcf A = MatrixXcf::Random(4,4);
+cout << "Here is a random 4x4 matrix, A:" << endl << A << endl << endl;
+ComplexSchur<MatrixXcf> schurOfA(A, false); // false means do not compute U
+cout << "The triangular matrix T is:" << endl << schurOfA.matrixT() << endl;