你如何改变Eigen中的Block？

Question

我无法重新分配Block。在下面的代码中，我以两种不同的方式存储矩阵A：

1. 为3 ArrayXd s，每行一个
2. 作为ArrayXXd

// data

ArrayXXd A (3, 3);
A << 0, 1, 2, 3, 4, 5, 6, 7, 8;

std::vector<ArrayXd> A_rows = {A.row(0), A.row(1), A.row(2)};

// std::vector<ArrayXd> solution

// first row
ArrayXd & current_row = A_rows[0];
// read it, write it, do stuff
// start working with the second row
current_row = std::ref(A_rows[1]);
cout << current_row << endl << endl; // prints 3 4 5
cout << A << endl; // A is unchanged

// Eigen solution

// first row
Block<ArrayXXd, 1, -1> && current_row_block = A.row(0);
// read it, write it, do stuff
// start working with the second row
current_row_block = std::ref(A.row(1)); // doesn't compile
cout << current_row_block << endl;
cout << A << endl;

错误消息是：

error: use of deleted function 'void std::ref(const _Tp&&) [with _Tp = Eigen::Block<Eigen::Array<double, -1, -1>, 1, -1, false>]'
 current_row_block = std::ref(A.row(1));
                                      ^

是否可以修复第二种方法，还是应该将矩阵存储为std::vector<ArrayXd>？

相关问题：Passing a reference of a vector element to a threaded function

Answer 1

您不需要Block<...>来引用一行。你只需要一个索引。

int current_row_id = 0;
std::out << A.row(current_row_id) << std::end;
current_row_id = 1;
std::out << A.row(current_row_id) << std::end;

对于std::vector<ArrayXd>方法，由于您要复制行，因此无法更改原始A。