c++ - 采用 VectorXf 并可以修改其值的函数

Question

我想了解如何操作特征向量/矩阵。我想实现最小二乘高斯牛顿算法(因此我学习使用 Eigen 库)。我有一个 1x6 的参数 vector ，每次迭代都需要更新它们。现在，我只想弄清楚函数如何将 vector 作为参数并更改其值...

Eigen::VectorXf betas = Eigen::VectorXf::Zero(6);

void SomeFunc(const Eigen::VectorXf& v){  // as per the Eigen guide, one must pass as const
    v(0) = 5;  // error: expression must be a modifiable lvalue
    return;
}

int main()
{
    betas(5) = 5.f;  // works
    SomeFunc(&betas);
    std::cout << "Hello World" << std::endl;
    std::cout << betas(0) << "\t" << betas(5) << std::endl;
}

我的问题是:如何让一个函数接受一个 vector 并修改它的值？

编辑:Eigen guide

Answer 1

正如文档所说:

Functions taking writable (non-const) parameters must take const references and cast away constness within the function body.

---

How would you make a function take a vector and modify its values?

您可以使用 const_cast 如下所示:

Eigen::VectorXf betas = Eigen::VectorXf::Zero(6);

void SomeFunc(const Eigen::VectorXf& v){  // as per the Eigen guide, one must pass as const
    const_cast<Eigen::VectorXf&>(v)(0) = 5;//cons_cast used here
    return;
}

int main()
{
    betas(5) = 5.f;  // works
    SomeFunc(betas);
    std::cout << "Hello World" << std::endl;
    std::cout << betas(0) << "\t" << betas(5) << std::endl;
}