Question

我正在尝试编写一个程序来计算n体问题。我试图改变我的代码遇到了一个问题，因此很容易适应任何数量的机构。函数corr（）似乎存在问题，在使用函数corr（）之后，对此函数中类粒子实例的某些变量所做的更改似乎会丢失。我该如何解决这个问题？

#include <cstdlib>
#include <iostream>
#include <cmath>
#include <fstream>
#define h  1000.0
#define G  6.67384*pow(10.0,-11)

using namespace std;


class particle{
      public:
      double kx1,kx2,kx3,kx4, kv1, kv2, kv3, kv4;
      double ky1, ky2, ky3, ky4, kvy1, kvy2, kvy3, kvy4;
      double x,y,vx,vy,m;


      double dist(particle aap){
             double dx = x - aap.x;
             double dy = y - aap.y;
             return sqrt(pow(dx,2.0)+pow(dy,2.0));
             }

      double g(double x1, double y1,particle aap){
             return G*aap.m*(aap.x-x1)/pow(dist(aap),3.0);
             }

      double p(double x1, double y1, particle aap){
             return G*aap.m*(aap.y-y1)/pow(dist(aap),3.0);
       }


      void update(){            //zet het object 1 stap vooruit
           x = x + (1/6.0)*(kx1+2*kx2+2*kx3+kx4);
           vx = vx + (1/6.0)*(kv1+2*kv2+2*kv3+kv4);
           y = y + (1/6.0)*(ky1+2*ky2+2*ky3+ky4);
           vy = vy + (1/6.0)*(kvy1+2*kvy2+2*kvy3+kvy4);
           }

     void create(double x1, double y1, double vx1, double vy1, double m1){
                      x = x1;
                      y = y1;
                      vx = vx1;
                      vy = vy1;
                      m =m1;
                      }

     bool operator ==(particle &other){
          if(x == other.x && y == other.y && vx == other.vx && vy == other.vy){
               return true;
               }
               }


      };



particle zon, maan, aarde;

void set(){
     zon.create(1, 1, -2, 1, 2*pow(10.0,30));
     aarde.create(1.5*pow(10.0,11), 0, 2, 29780, 6*pow(10.0,24));
     maan.create(aarde.x + 1, aarde .y + 3.844399*pow(10.0,8), aarde.vx +  -1022.0, aarde.vy + 1, 7.3347*pow(10.0,22));
     }



double xforce(double x1, double y1, particle aap){     //kracht in de x-richting 

       particle bodies[] = {zon, aarde, maan};

       double fx;
       for (int i = 0; i < 3; i++){
           if (bodies[i].x == aap.x && bodies[i].y == aap.y && bodies[i].vx == aap.vx && bodies[i].vy == aap.vy ){;}

           else{
                fx += aap.g(x1,y1,bodies[i]);
                }
                }
       return fx;
       }

double yforce(double x1, double y1, particle aap){ //kracht in de y-richting 

       particle bodies[] = {zon, aarde, maan};

       double fy;
       for (int i = 0; i <= 3; i++){
           if (bodies[i].x == aap.x && bodies[i].y == aap.y && bodies[i].vx == aap.vx && bodies[i].vy == aap.vy) {;}

           else{
                fy += aap.p(x1,y1,bodies[i]);
                }
                }
       return fy;
       }


void corr(particle body){
     body.kx1 = h*body.vx;
     body.kv1 = h*xforce(body.x, body.y, body);
     body.ky1 = h*body.vy;
     body.kvy1 =h*yforce(body.x, body.y, body);

     body.kx2 = h*(body.vx + 0.5*body.kv1);
     body.kv2 = h*xforce(body.x + 0.5*body.kx1, body.y + 0.5*body.ky1, body);
     body.ky2 = h*(body.vy + 0.5*body.kvy1);
     body.kvy2 = h*yforce(body.x + 0.5*body.kx1, body.y + 0.5*body.ky1, body);

     body.kx3 = h*(body.vx+ 0.5*body.kv2);
     body.kv3 = h*xforce(body.x + 0.5*body.kx2, body.y + 0.5*body.ky2, body);
     body.ky3 = h*(body.vy+ 0.5*body.kvy2);
     body.kvy3 = h*yforce(body.x + 0.5*body.kx2, body.y + 0.5*body.ky2,body);

     body.kx4 = h*(body.vx+body.kv3);
     body.kv4 = h*xforce(body.x+ body.kx3, body.y + body.ky3, body);
     body.ky4 = h*(body.vy + body.kvy3);
     body.kvy4 = h*yforce(body.x + body.kx3, body.y + body.ky3, body);
     }







void bereken(){
     set();
     ofstream file;
     file.open("3body.txt");
     for(int i =0; i <=30000; i++){
             corr(maan);
             corr(zon);
             corr(aarde);
             zon.update();
             aarde.update();
             maan.update();
             file << i*h <<"  "<< zon.x << "  "<< zon.y << "    "<< zon.vx<< "  "<< zon.vy <<"  "<< aarde.x << "    " << aarde.y <<"    "<< aarde.vx <<"    " << aarde.vy <<"   "<< maan.x<<"  "<<maan.y<<"\n";
             }
     file.close();
     }


int main()
{   
    set();
    bereken();
    system("pause");
    return 0;

}

Answer 1

只需使用参考：

void corr(particle& body)

必须在其他地方应用相同的修复程序。您目前拥有的代码是 COPIES 您的对象，对其执行一些计算然后只删除此临时对象...通过使用引用（&），您可以有效地“共享”调用者和被调用者之间的对象。

在你的类方法中你也应该使用引用传递这个对象，但这次出于效率原因 - 传递引用很简单（通常与指针相同），但复制这个巨大的对象需要时间。

Answer 2

Freddie Chopin提出的建议工作并修复了函数corr（）。然而，现在我发现函数xforce（）和yforce（）不能正常工作。它们应该返回某个粒子上的总力，这是他们在第一步中所做的，但在此之后它们似乎返回了错误的值。任何人都知道为什么会这样？

C ++更改实例变量

2 个答案: