initial commit

third_party/eigen/doc/examples/make_circulant.cpp.expression

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+template <class ArgType>
+class Circulant : public Eigen::MatrixBase<Circulant<ArgType> > {
+ public:
+  Circulant(const ArgType& arg) : m_arg(arg) {
+    EIGEN_STATIC_ASSERT(ArgType::ColsAtCompileTime == 1, YOU_TRIED_CALLING_A_VECTOR_METHOD_ON_A_MATRIX);
+  }
+
+  typedef typename Eigen::internal::ref_selector<Circulant>::type Nested;
+
+  typedef Eigen::Index Index;
+  Index rows() const { return m_arg.rows(); }
+  Index cols() const { return m_arg.rows(); }
+
+  typedef typename Eigen::internal::ref_selector<ArgType>::type ArgTypeNested;
+  ArgTypeNested m_arg;
+};