eigen/doc/examples/make_circulant.cpp.evaluator

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namespace Eigen {
namespace internal {
template <typename ArgType>
struct evaluator<Circulant<ArgType> > : evaluator_base<Circulant<ArgType> > {
typedef Circulant<ArgType> XprType;
typedef typename nested_eval<ArgType, XprType::ColsAtCompileTime>::type ArgTypeNested;
typedef remove_all_t<ArgTypeNested> ArgTypeNestedCleaned;
typedef typename XprType::CoeffReturnType CoeffReturnType;
enum { CoeffReadCost = evaluator<ArgTypeNestedCleaned>::CoeffReadCost, Flags = Eigen::ColMajor };
evaluator(const XprType& xpr) : m_argImpl(xpr.m_arg), m_rows(xpr.rows()) {}
CoeffReturnType coeff(Index row, Index col) const {
Index index = row - col;
if (index < 0) index += m_rows;
return m_argImpl.coeff(index);
}
evaluator<ArgTypeNestedCleaned> m_argImpl;
const Index m_rows;
};
} // namespace internal
} // namespace Eigen