Eigen

Question

以下代码将一个由 1 组成的向量连接到一个矩阵：

using Eigen::VectorXd;
using Eigen::MatrixXd;

MatrixXd cbind1(const Eigen::Ref<const MatrixXd> X) {
  const unsigned int n = X.rows();
  MatrixXd Y(n, 1 + X.cols());
  Y << VectorXd::Ones(n), X;
  return Y;
}

该函数将 X 的内容复制到 Y。我如何定义该函数以避免进行复制和 returns 对包含 VectorXd::Ones(n), X 的矩阵的引用？

谢谢。

Answer 1

如果您关注并阅读了 ggael 对您的 (and it appears you did, as you accepted his answer), you would have read this page of the docs. By modifying the example slightly, you could have written as part of an MCVE 的回答：

#include <iostream>
#include <Eigen/Core>

using namespace Eigen;

template<class ArgType>
struct ones_col_helper {
    typedef Matrix<typename ArgType::Scalar,
        ArgType::SizeAtCompileTime,
        ArgType::SizeAtCompileTime,
        ColMajor,
        ArgType::MaxSizeAtCompileTime,
        ArgType::MaxSizeAtCompileTime> MatrixType;
};

template<class ArgType>
class ones_col_functor
{
    const typename ArgType::Nested m_mat;

public:
    ones_col_functor(const ArgType& arg) : m_mat(arg) {};

    const typename ArgType::Scalar operator() (Index row, Index col) const {
        if (col == 0) return typename ArgType::Scalar(1);
        return m_mat(row, col - 1);
    }
};

template <class ArgType>
CwiseNullaryOp<ones_col_functor<ArgType>, typename ones_col_helper<ArgType>::MatrixType>
cbind1(const Eigen::MatrixBase<ArgType>& arg)
{
    typedef typename ones_col_helper<ArgType>::MatrixType MatrixType;
    return MatrixType::NullaryExpr(arg.rows(), arg.cols()+1, ones_col_functor<ArgType>(arg.derived()));
}

int main()
{
    MatrixXd mat(4, 4);
    mat << 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16;

    auto example = cbind1(mat);

    std::cout << example << std::endl;
    return 0;
}

Eigen - 级联矩阵作为参考

Eigen - Concatenated matrix as a reference

c++