c ++ nbody模拟传递数组作为参考

Question

在使用包含所有实体的数组时，尝试编写代码来解决nbody问题时遇到问题。我的代码没有做正确的事情，我不知道它出错的地方虽然我怀疑它与传递数组作为参考有关。为了更容易发现我的错误，我将包含一个工作版本的代码，它不会以相同的方式使用包含所有实体的数组。以下是不起作用的代码（使用此代码计算物体轨道而不是椭圆时）：

#include <cstdlib>
#include <iostream>
#include <cmath>
#include <fstream>
#define h  10000.0                  // size of the timestep
#define N  3                        // number of bodies
#define G  6.67384*pow(10.0,-11)    // gravitational constant

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

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

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


      void update(){                                      //object advances 1 step
           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){  //choose the inital conditions for a new object
                      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 bodies[N];


void set(particle (&bodies)[N]){
     bodies[0].create(1, 1, -2, 1, 2*pow(10.0,30));
     bodies[1].create(2870671*pow(10.0,6), 0, 0, 6800, 8.6810*pow(10.0,25));
     bodies[2].create(4498542*pow(10.0,6),0 ,0, 5430, 1.0243*pow(10.0,26));
     }


double xforce(double x1, double y1, particle body, particle bodies[N]){    //force in the x- direction

       double fx = 0;
       for (int i = 0; i < N; i++){
           if (bodies[i] == body ){;}

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

double yforce(double x1, double y1, particle body, particle bodies[N]){ //force in the y- direction 

       double fy = 0;
       for (int i = 0; i < N; i++){
           if (bodies[i] == body) {;}

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


void corr(double t, particle bodies[N]){                            //runge kutta 4
     for(int i =0; i <= N; i++){

            bodies[i].kx1 = t*bodies[i].vx;
            bodies[i].kv1 = t*xforce(bodies[i].x, bodies[i].y, bodies[i], bodies);
            bodies[i].ky1 = t*bodies[i].vy;
            bodies[i].kvy1 = t*yforce(bodies[i].x, bodies[i].y, bodies[i], bodies);

            bodies[i].kx2 = t*(bodies[i].vx + 0.5*bodies[i].kv1);
            bodies[i].kv2 = t*xforce(bodies[i].x + 0.5*bodies[i].kx1, bodies[i].y + 0.5*bodies[i].ky1, bodies[i], bodies);
            bodies[i].ky2 = t*(bodies[i].vy + 0.5*bodies[i].kvy1);
            bodies[i].kvy2 = t*yforce(bodies[i].x + 0.5*bodies[i].kx1, bodies[i].y + 0.5*bodies[i].ky1, bodies[i], bodies);

            bodies[i].kx3 = t*(bodies[i].vx+ 0.5*bodies[i].kv2);
            bodies[i].kv3 = t*xforce(bodies[i].x + 0.5*bodies[i].kx2, bodies[i].y + 0.5*bodies[i].ky2, bodies[i], bodies);
            bodies[i].ky3 = t*(bodies[i].vy+ 0.5*bodies[i].kvy2);
            bodies[i].kvy3 = t*yforce(bodies[i].x + 0.5*bodies[i].kx2, bodies[i].y + 0.5*bodies[i].ky2,bodies[i], bodies);

            bodies[i].kx4 = t*(bodies[i].vx + bodies[i].kv3);
            bodies[i].kv4 = t*xforce(bodies[i].x+ bodies[i].kx3, bodies[i].y + bodies[i].ky3, bodies[i], bodies);
            bodies[i].ky4 = t*(bodies[i].vy + bodies[i].kvy3);
            bodies[i].kvy4 = t*yforce(bodies[i].x + bodies[i].kx3, bodies[i].y + bodies[i].ky3, bodies[i], bodies);
            }
     }


void calculate(particle (&bodies)[N]){
     set(bodies);
     ofstream file;
     file.open("tester.txt");
     for(int i =0; i <=50000; i++){

             corr(h, bodies);                          
             for(int j = 0; j <= N; j++){
                     bodies[j].update();
                     }                   
             if( i%1000 == 0){

                 file << i*h;
                 for(int j = 0; j <=N ; j++){
                          file <<"  "<<bodies[j].x << "  "<< bodies[j].y;
                          }
                 file <<"  "<<"\n";
                 }
             else{;}
             }
     file.close();
     }


int main()
{   
    calculate(bodies);
    system("pause");
    return 0;
}

这是代码的工作版本，两者都应该解决同样的问题：

#include <cstdlib>
#include <iostream>
#include <cmath>
#include <fstream>
#define h  10000.0
#define N  3
#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 body){
             double dx = x - body.x;
             double dy = y - body.y;
             return sqrt(pow(dx,2.0)+pow(dy,2.0));
             }

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

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


      void update(){            
           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;
               }
               }

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



particle zon, uranus, neptunus;
particle closest[] = {uranus, neptunus};



void set(){
     zon.create(1, 1, -2, 1, 2*pow(10.0,30));
     uranus.create(2870671*pow(10.0,6), 0, 0, 6800, 8.6810*pow(10.0,25));
     neptunus.create(4498542*pow(10.0,6),0 ,0, 5430, 1.0243*pow(10.0,26));
     }


double xforce(double x1, double y1, particle body){    

       particle bodies[] = {zon, uranus, neptunus};

       double fx = 0;
       for (int i = 0; i < 3; i++){
           if (bodies[i] == body ){;}

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

double yforce(double x1, double y1, particle body){ 

       particle bodies[] = {zon, uranus, neptunus};

       double fy = 0;
       for (int i = 0; i <= 3; i++){
           if (bodies[i] == body) {;}

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


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

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

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

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







void bereken(){
     set();
     ofstream file;
     file.open("tester.txt");
     for(int i =0; i <=50000; i++){
             corr(zon, h);
             corr(uranus, h);
             corr(neptunus, h);

             zon.update();
             uranus.update();
             neptunus.update();

             if( i%1000 == 0){             
                 file << i*h <<"  "<<zon.x << "  "<< zon.y <<"    "<<uranus.x<<"    " <<uranus.y <<"   "<< neptunus.x<<"  "<<neptunus.y<<"   "<<"\n";
                 }
             else{;}
             }
     file.close();
     }


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

Answer 1

一个问题是你在3个地方溢出bodies[]数组：

#define N  3   
particle bodies[N];

for (int i = 0; i <= N; i++) {
    bodies[i].x = ...  // Oops, access bodies[3] which doesn't exist

您在两个地方使用的正确循环是：

for (int i = 0; i < N; i++) {  // 0 to < N