避免在特征中用对角线矩阵分配
问题
如何避免特征中小对角矩阵的动态分配？
上下文
我正在使用 Eigen 3.4。我有一个 N × N 对角矩阵 W：
auto W = Eigen::DiagonalMatrix<double, Dynamic>(N);
如果 N <= 512，我想通过使用堆栈上的缓冲区来避免分配：
double W_buffer[512];
对于法线向量和矩阵，我知道我可以使用 Map ：
double y_buff[512];
auto y = Eigen::Map<VectorXd>( y_buff, N );
但是，当我对对角矩阵尝试相同的操作时，它会给我一个错误，因为 InnerStrideAtCompileTime 不是特征::对角矩阵。
将 Map 与 DiagonalMatrix 结合使用时出现错误消息
In file included from eigen/Eigen/Core:311,
from eigen/Eigen/Dense:1,
from build/release/CMakeFiles/bench.dir/cmake_pch.hxx:5,
from <command-line>:
eigen/Eigen/src/Core/Map.h: In instantiation of ‘struct Eigen::internal::traits<Eigen::Map<Eigen::DiagonalMatrix<double, -1> > >’:
eigen/Eigen/src/Core/util/ForwardDeclarations.h:34:48: required from ‘struct Eigen::internal::accessors_level<Eigen::Map<Eigen::DiagonalMatrix<double, -1> > >’
eigen/Eigen/src/Core/util/ForwardDeclarations.h:101:75: required from ‘class Eigen::Map<Eigen::DiagonalMatrix<double, -1> >’
include/volar/estimators.hpp:203:18: required from ‘static volar::R volar::PolyLE<Degree>::estimate(volar::R, volar::ViewR, volar::ViewR, const Kernel&) [with Kernel = volar::UniformK; int Degree = 1; volar::R = double; volar::ViewR = volar::View<double>]’
include/volar/kernel_smoothing.hpp:81:64: required from ‘volar::R volar::LocalRFT<Estimator, Kernel>::operator()(volar::R) const [with Estimator = volar::EigenLinearLE; Kernel = volar::UniformK; volar::R = double]’
bench/core.cpp:43:23: required from ‘void localRF(benchmark::State&) [with Method = volar::EigenLinearLE; Kernel = volar::UniformK]’
bench/core.cpp:96:1: required from here
eigen/Eigen/src/Core/Map.h:30:53: error: ‘InnerStrideAtCompileTime’ is not a member of ‘Eigen::DiagonalMatrix<double, -1>’
30 | ? int(PlainObjectType::InnerStrideAtCompileTime)
| ^~~~~~~~~~~~~~~~~~~~~~~~
In file included from eigen/Eigen/Core:163,
from eigen/Eigen/Dense:1,
from build/release/CMakeFiles/bench.dir/cmake_pch.hxx:5,
from <command-line>:
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评论（2）
Eigen::DiagonalMatrix的第三个模板参数MaxSizeAtCompileTime可以让您做到这一点。与
Eigen::Dynamic结合使用时，DiagonalMatrix将具有足够大的内部缓冲区以容纳MaxSizeAtCompileTime，但其大小仍会动态调整。例如，以下内容与您尝试对外部缓冲区执行的操作等效：
显然，尝试使用大于 MaxSizeAtCompileTime 的大小对其进行初始化将在运行时失败（使用断言），但是这并不比您使用
Map时必须处理的情况更糟糕。The third template parameter of
Eigen::DiagonalMatrix,MaxSizeAtCompileTimelets you do just that.When combined with
Eigen::Dynamic, theDiagonalMatrixwill have an internal buffer large enough forMaxSizeAtCompileTime, but it will still be dynamically sized.For example, the following is the equivalent of what you were trying to do with an external buffer:
Obviously, attempting to initialize it with a size greater than
MaxSizeAtCompileTimewill fail at runtime (with an assert), but that's not any worse than what you have to deal with when usingMap.而不是尝试
MAPaDiagonalMatrix您可以以“正常”方式来描述和使用asdiagonal（）方法。也许必须少一些干净才能键入
y.asdiagonal（）而不是y...也许您可以使用eigen :: ref 请参考来自您的向量的对角线矩阵，但我不确定是否可以使用。asdiagonal（）：Instead of trying to
MapaDiagonalMatrixyou can do it the "normal" way that you describe and use theasDiagonal()method.Maybe slightly less clean to have to type
y.asDiagonal()instead of justy...Maybe you could do something withEigen::Refto keep a reference to the diagonal matrix that came from your vector but I'm not sure if that would work.asDiagonal():https://eigen.tuxfamily.org/dox/classEigen_1_1MatrixBase.html#a14235b62c90f93fe910070b4743782d0