向量不是可递增的错误

Question

我正在用C++编写一个实现Newton-Raphson方法的程序,除此之外,还定义了一个多项式类:

#include <iostream>
#include <algorithm>
#include <utility>
#include <string>
#include <cmath>
#include <vector>
#include <set>

using namespace std;

class polynomial{

    using pair_dd = pair<double, double>;

public:
    polynomial(const vector<pair_dd>& v) : m_coeff(simplify(v)) {} // constructor
    polynomial(const polynomial& p) : m_coeff(p.m_coeff){} // copy constructor
    polynomial derivative() const{ // computes derivative
        vector<pair_dd> dcoeff;
        for_each(begin(m_coeff), end(m_coeff), [&](pair_dd p){
            dcoeff.emplace_back(pair_dd(p.first*p.second, p.second - 1));
        });
        return polynomial(dcoeff);
    }
    double apply(double x) const{ // applies poly to argument
        auto sum(0.0);
        for_each(begin(m_coeff), end(m_coeff), [&](pair_dd p){
            sum += p.first*pow(x, p.second);
        });
        return sum;
    }
    void write() const{ // prints polynomial
        // function just for testing
        for (const auto& term : m_coeff)
            cout << term.first << "x^" << term.second << " +";
        cout << endl;
    }

private:
    polynomial(); //forbid empty constructor
    vector<pair_dd> m_coeff;
    vector<pair_dd> simplify(const vector<pair_dd>& v) const{

        set<double> exp; // set of exponents
        for (const auto& term : v)
            exp.insert(term.second);

        vector<pair_dd> ret; // final simplified vector
        vector<pair_dd> temp; // temporary object

        for (const auto& power : exp){
            copy_if(begin(v), end(v), begin(temp), [&](const pair_dd p){
                return (p.second == power);
            });
            // combine terms
            auto sum(0.0);
            for (auto& p : temp)
                sum += p.first;
            ret.push_back(pair_dd(sum, power));
            temp.clear();
        }
        return ret;
    }
};


int main(){

    vector<pair<double, double>> vec;
    vec.push_back(pair<double, double>(5,1)); // 5x
    vec.push_back(pair<double, double>(10, 1)); // 10x
    vec.push_back(pair<double, double>(3, 2)); // 3x^2

    polynomial poly(vec);

    // should write 15x + 3x^2

    poly.write();
    return 0;
}

我遇到的问题是simplify在运行期间导致错误的功能copy_if.据说是的

矢量temp不可递增

在Visual Studio中.我的算法的工作方式是通过在一个集合中收集具有相同x的幂的所有项(因为我们只需要唯一的元素).随后,我迭代指数集,使用copy_if对的向量将所有具有相同指数的项组合在一起,然后将它们组合并放入最终向量中.

我已经尝试了保留和调整临时矢量的大小.

Answer 1

copy_if不会分配内存,它假设temp已经是大小,而不是.您可以使用std::back_inserter出来的<iterator>.

copy_if(begin(v), end(v), back_inserter(temp), [&](const pair_dd p){
    return (p.second == power);
});