#include <Eigen/Core>
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#include <iostream>
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using namespace Eigen;
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// [circulant_func]
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template<class ArgType>
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class circulant_functor {
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const ArgType &m_vec;
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public:
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circulant_functor(const ArgType& arg) : m_vec(arg) {}
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const typename ArgType::Scalar& operator() (Index row, Index col) const {
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Index index = row - col;
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if (index < 0) index += m_vec.size();
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return m_vec(index);
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}
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};
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// [circulant_func]
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// [square]
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template<class ArgType>
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struct circulant_helper {
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typedef Matrix<typename ArgType::Scalar,
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ArgType::SizeAtCompileTime,
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ArgType::SizeAtCompileTime,
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ColMajor,
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ArgType::MaxSizeAtCompileTime,
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ArgType::MaxSizeAtCompileTime> MatrixType;
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};
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// [square]
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// [makeCirculant]
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template <class ArgType>
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CwiseNullaryOp<circulant_functor<ArgType>, typename circulant_helper<ArgType>::MatrixType>
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makeCirculant(const Eigen::MatrixBase<ArgType>& arg)
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{
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typedef typename circulant_helper<ArgType>::MatrixType MatrixType;
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return MatrixType::NullaryExpr(arg.size(), arg.size(), circulant_functor<ArgType>(arg.derived()));
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}
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// [makeCirculant]
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// [main]
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int main()
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{
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Eigen::VectorXd vec(4);
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vec << 1, 2, 4, 8;
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Eigen::MatrixXd mat;
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mat = makeCirculant(vec);
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std::cout << mat << std::endl;
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}
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// [main]
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