Question

我正在努力让我的方法发挥作用。我是C ++的初学者。我试图找到两个向量的点积。我在for循环中遇到一些错误。有人可以帮帮我吗。

float dot(Matrixf const& vec1, Matrixf const& vec2) {

    // error check
    if (!vec1.isVector() || !vec2.isVector()) {
        throw std::runtime_error("Unable to do dot product: not column vectors.");
    }
    if (vec1.nrows() != vec2.nrows()) {
        throw std::runtime_error("Unable to do dot product: vector lengths not equal.");
    }

    /** implementing dot product *************************************/

    float ret = 0;

    for(unsigned i = 0; i < vec1.ncols(); ++i){
        for(unsigned j =0; j< vec2.nrows(); ++j){
        ret += vec1[i] * vec2[j];

}
    }
    return ret;
}

Matrixf类

#include "matrixf.h"

#include <iostream>

Matrixf::Matrixf(unsigned int rows, unsigned int cols) {
    rows_ = rows;
    cols_ = cols;
    data_ = new float[rows_ * cols_];

    // set all initial values to zero
    for (unsigned int r = 0; r < rows_; ++r) {
        for (unsigned int c = 0; c < cols_; ++c) {
            data_[r * cols_ + c] = 0;
        }
    }
}

Matrixf::~Matrixf() {
    delete data_;
}

Matrixf::Matrixf(Matrixf const& other) {
    rows_ = other.rows_;
    cols_ = other.cols_;
    data_ = new float[rows_ * cols_];
    for (unsigned int i = 0; i < rows_ * cols_; ++i) {
        data_[i] = other.data_[i];
    }
}

Matrixf& Matrixf::operator=(Matrixf const& other) {
    // handles self assignment
    if (this == &other) {
        return *this;
    }

    delete data_;
    rows_ = other.rows_;
    cols_ = other.cols_;
    data_ = new float[rows_ * cols_];
    for (unsigned int i = 0; i < rows_ * cols_; ++i) {
        data_[i] = other.data_[i];
    }
    return *this;
}

float Matrixf::get(unsigned int row, unsigned int col) const {
#ifndef NDEBUG
    if (row >= rows_ || col >= cols_) {
        throw std::runtime_error("Matrix index out of bounds.");
    }
#endif

    return data_[row * cols_ + col];
}

void Matrixf::set(unsigned int row, unsigned int col, float val) {
#ifndef NDEBUG
    if (row >= rows_ || col >= cols_) {
        throw std::runtime_error("Matrix index out of bounds.");
    }
#endif
    data_[row * cols_ + col] = val;
}

float& Matrixf::operator()(unsigned int row, unsigned int col) {
    return data_[row * cols_ + col];
}

float Matrixf::operator()(unsigned int row, unsigned int col) const {
    return data_[row * cols_ + col];
}

unsigned int Matrixf::nrows() const {
    return rows_;
}

unsigned int Matrixf::ncols() const {
    return cols_;
}

bool Matrixf::isVector() const {
    return (cols_ == 1);
}

Matrixf Matrixf::eye(unsigned int size) {
    Matrixf e(size, size);
    for (unsigned int i = 0; i < size; ++i) {
        e.set(i, i, 1);
    }

    return e;
}

std::ostream& operator << (std::ostream& os, Matrixf const& matrix) {
    for (unsigned int r = 0; r < matrix.nrows(); ++r) {
        for (unsigned int c = 0; c < matrix.ncols(); ++c) {
            os << matrix.data_[r * matrix.cols_ + c] << " ";
        }
        os << "\n";
    }

    return os;
}

Answer 1

我想你只想要一个循环：

for(unsigned i = 0; i < vec1.ncols(); ++i){
  ret += vec1[i] * vec2[i];
}

我还注意到你比较

vec1.nrows() != vec2.nrows()

但你在循环中使用ncols()。你想要哪一个？

Answer 2

我从你的另一个问题中看到你写了一个光线追踪器。

在光线跟踪器中，通常情况下，你总是为矢量和矩阵提供单独的数据结构，因为它们几乎总是以不同的方式使用，编程中的专业化几乎总能带来更快的代码。

如果您然后仅为矢量定义点积，则点积代码将变得简单。

C ++中的Dot产品实现

2 个答案: