make_circulant2.cpp
68bb631292e1master

make_circulant2.cpp
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			#include <Eigen/Core>
			#include <iostream>

			using namespace Eigen;

			// [circulant_func]
			template<class ArgType>
			class circulant_functor {
			const ArgType &m_vec;
			public:
			circulant_functor(const ArgType& arg) : m_vec(arg) {}

			const typename ArgType::Scalar& operator() (Index row, Index col) const {
			Index index = row - col;
			if (index < 0) index += m_vec.size();
			return m_vec(index);
			}
			};
			// [circulant_func]

			// [square]
			template<class ArgType>
			struct circulant_helper {
			typedef Matrix<typename ArgType::Scalar,
			ArgType::SizeAtCompileTime,
			ArgType::SizeAtCompileTime,
			ColMajor,
			ArgType::MaxSizeAtCompileTime,
			ArgType::MaxSizeAtCompileTime> MatrixType;
			};
			// [square]

			// [makeCirculant]
			template <class ArgType>
			CwiseNullaryOp<circulant_functor<ArgType>, typename circulant_helper<ArgType>::MatrixType>
			makeCirculant(const Eigen::MatrixBase<ArgType>& arg)
			{
			typedef typename circulant_helper<ArgType>::MatrixType MatrixType;
			return MatrixType::NullaryExpr(arg.size(), arg.size(), circulant_functor<ArgType>(arg.derived()));
			}
			// [makeCirculant]

			// [main]
			int main()
			{
			Eigen::VectorXd vec(4);
			vec << 1, 2, 4, 8;
			Eigen::MatrixXd mat;
			mat = makeCirculant(vec);
			std::cout << mat << std::endl;
			}
			// [main]