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用eigen3库编写一个以转置为参数的函数

eigen3 eigen c++

R zu · 技术社区 · 7 年前

密集阵列/矩阵,或
密集数组/矩阵的转置。

有没有可能避免使用完美转发?

我试过使用 DenseBase 类型参数。但这不能接受矩阵的转置。

当前解决方案:

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

using namespace Eigen;

template <typename U>
auto f(U&& x) {
    auto x2 = std::forward<U>(x);
    auto max_x = x2.colwise().maxCoeff().eval();
    x2 = x2.rowwise() + max_x;
    return max_x;
}

int main() {
    Array<float, 3, 3> M1;
    M1 << 1, 2, 3, 
          4, 5, 6, 
          7, 8, 9;
    std::cout << M1 << "\n";
    // auto here might cause problem later ...
    // see eigen.tuxfamily.org/dox/TopicPitfalls.html
    auto max_x = f(M1.transpose());
    std::cout << M1 << "\n";
    std::cout << max_x << "\n";
}

结果:

// original
1 2 3
4 5 6
7 8 9
// Increase each row by max of the row.
 4  5  6
10 11 12
16 17 18
// Max of each row (not a column vector).
3 6 9

我试过了 EigenBase 使用以下行:

template <typename U>
auto f(EigenBase<U>& x) {
...

test4.cpp:20:32: error: cannot bind non-const lvalue reference of type âEigen::EigenBase<Eigen::Transpose<Eigen::Array<float, 3, 3> > >&â to an rvalue of type âEigen::EigenBase<Eigen::Transpose<Eigen::Array<float, 3, 3> > >â
     auto max_x = f(M1.transpose());
                    ~~~~~~~~~~~~^~

2 回复 | 直到 7 年前

R zu 7 年前

用左值引用和右值引用参数重载函数似乎可以解决这个问题。

我怀疑转置是唯一生成临时c++表达式的东西。如果我希望转置版本返回一个转置结果(列而不是行向量),而非转置版本返回一个非转置结果,这就不能解决这个问题。

谢谢 kmdreko

测试:

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

using namespace Eigen;

template <typename Derived>
auto f(DenseBase<Derived>& x) {
    auto max_x = x.colwise().maxCoeff().eval();
    x = x.rowwise() + max_x;
    return max_x;
}

template <typename Derived>
auto f(DenseBase<Derived>&& x) {
    return f(x).transpose().eval();
}

int main() {
    Array<float, 3, 3> M1, M2;
    M1 << 1, 2, 3, 
          4, 5, 6, 
          7, 8, 9;
    M2 = M1;
    std::cout << M1 << "\n";

    std::cout << "no transpose\n";
    Array<float, 3, 1> max_x = f(M1);
    std::cout << M1 << "\n";
    std::cout << max_x << "\n";

    std::cout << "transpose\n";
    Array<float, 1, 3> max_x2 = f(M2.transpose());
    std::cout << M2 << "\n";
    std::cout << max_x2 << "\n";
}

结果:

1 2 3
4 5 6
7 8 9
no transpose
 8 10 12
11 13 15
14 16 18
// returns column vector
7
8
9
transpose
 4  5  6
10 11 12
16 17 18
// returns row vector
3 6 9

R zu 7 年前

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

using namespace Eigen;

template <typename Derived>
auto f(DenseBase<Derived>& x) {
    auto max_x = x.colwise().maxCoeff().eval();
    x = x.rowwise() + max_x;
    return max_x;
}

int main() {
    Array<float, 3, 3> M1, M2;
    M1 << 1, 2, 3, 
          4, 5, 6, 
          7, 8, 9;
    M2 = M1;
    std::cout << M1 << "\n";

    std::cout << "no transpose\n";
    Array<float, 3, 1> max_x = f(M1);
    std::cout << M1 << "\n";
    std::cout << max_x << "\n";

    std::cout << "transpose\n";
    auto m2_t = M2.transpose();
    Array<float, 1, 3> max_x2 = f(m2_t);
    std::cout << M2 << "\n";
    std::cout << max_x2 << "\n";
}

结果:

1 2 3
4 5 6
7 8 9
no transpose
 8 10 12
11 13 15
14 16 18
7
8
9
transpose
 4  5  6
10 11 12
16 17 18
3 6 9