我撕我的头发试图在Eigen::Tensor<double, 3>
作为Eigen::VectorXd
访问数据的列。
切片,as according to this answer,做工精细,让我我想要的列。但我不能然后分配到一个载体。
我有的:
Eigen::Tensor<double, 3> my_tens(2, 3, 4);
my_tens.setRandom();
Eigen::array<Eigen::Index, 3> dims = my_tens.dimensions();
Eigen::array<Eigen::Index, 3> offsets = {0, 1, 0};
Eigen::array<Eigen::Index, 3> extents = {dims[0], 1, 1};
// This works perfectly, and is exactly the column I want:
std::cout << my_tens.slice(offsets, extents);
// ... and I want it as a VectorXd, so:
Eigen::VectorXd my_vec(dims[0]);
下面的事情我已经尝试了所有失败:
// Direct assignment (won't compile, no viable overloaded '=')
my_vec = my_tens.slice(offsets, extents);
// Initialisation (won't compile, no viable overloaded '<<')
my_vec << my_tens.slice(offsets, extents);
// Same problem with reshaping:
g_a = signature_a.g.slice(offsets, extents).reshape(Eigen::array<Eigen::Index, 2>{dims[0], 1});
// Converting the base (won't compile, no member 'matrix')
my_vec << my_tens.slice(offsets, extents).matrix();
我也试过映射as in this answer,但是,这并不工作,要么(编辑:我认为这是由于到存储排序,但实际上是由于不正确的偏移量,请看我的回答):
// This produces a part of a row of the tensor, not a column. Gah!
auto page_offset = offsets[2] * dims[0] * dims[1];
auto col_offset = offsets[1] * dims[0];
auto bytes_offset = sizeof(double) * (page_offset + col_offset)
Eigen::Map<Eigen::VectorXd> my_mapped_vec(my_tens.data() + bytes_offset, dims[0]);
如果真的这么难,还是我失去了一些东西简单?感谢您的任何和所有帮助!
回答我的问题:是的,我失去了一些东西简单。通过对比数字我下了地图操作的我意识到的偏移量为8出的一个因素;即通过出sizeof(double)
。
我没有意识到该操作my_tens.data() + bytes_offset
需要my_tens.data()
,一个const double *
,和而不是添加字节固定数量的,以抵消指针,由该数量的元件的偏移它。
下面是正确的代码:
Eigen::Tensor<double, 3> my_tens(2, 3, 4);
my_tens.setRandom();
Eigen::array<Eigen::Index, 3> dims = my_tens.dimensions();
Eigen::array<Eigen::Index, 3> offsets = {0, 1, 0};
Eigen::array<Eigen::Index, 3> extents = {dims[0], 1, 1};
// Compute the offset, correctly this time!
auto page_offset = offsets[2] * dims[0] * dims[1];
auto col_offset = offsets[1] * dims[0];
auto elements_offset = page_offset + col_offset;
// Map into the array
Eigen::Map<Eigen::VectorXd> my_mapped_vec(my_tens.data() + elements_offset, dims[0]);
// Compare the two:
std::cout << my_tens.slice(offsets, extents) << std::endl;
std::cout << my_mapped_vec.transpose() << std::endl;