4m_lab2_s2

// 4m_lab2.cpp: определяет точку входа для консольного приложения.
//

#include "stdafx.h"//vs2010
#include <bits\stdc++.h>
#include "gnuplot_i.hpp"
#include <conio.h>
#include <windows.h>

using namespace std;

#define cyrillic setlocale(LC_CTYPE, "rus")

const string path1 = "C:\\Users\\Admin\\Documents\\Visual Studio 2010\\Projects\\4m_lab2\\1.txt";
const string path2 = "C:\\Users\\Admin\\Documents\\Visual Studio 2010\\Projects\\4m_lab2\\2.txt";

inline string dtos(double d){ostringstream strs; strs << d; return strs.str();}

double f(double x , double y);
double g(double x , double y);

void wait(){
    FlushConsoleInputBuffer(GetStdHandle(STD_INPUT_HANDLE));
    #ifndef FOUT
        cout << endl << "Press any key to continue..." << endl;
    #endif
    _getch();
}

vector<pair<double , pair<double , double> > > Runge_Kutta1(double x_ , double y_ , double n , double max_t){
    double h = max_t / n;

    vector<pair<double , pair<double , double> > > v;
    v.push_back(make_pair(0 , make_pair(x_ , y_)));

    for(int i = 0 ; i < n ; ++i){
        double t = 1.0 * (i + 1) * h;

        x_ += h * f(x_ , y_);
        y_ += h * g(x_ , y_);

        v.push_back(make_pair(t , make_pair(x_ , y_)));
    }

    return v;
}

vector<pair<double , pair<double , double> > > Runge_Kutta4(double x_ , double y_ , double n , double max_t){
    double h = max_t / n;

    vector<pair<double , pair<double , double> > > v;
    v.push_back(make_pair(0 , make_pair(x_ , y_)));

    for(int i = 0 ; i < n ; ++i){
        double t = 1.0 * (i + 1) * h;

        double k1 = h * f(x_ , y_);
        double m1 = h * g(x_ , y_);

        double k2 = h * f(x_ + k1 / 2 , y_ + m1 / 2);
        double m2 = h * g(x_ + k1 / 2 , y_ + m1 / 2);

        double k3 = h * f(x_ + k2 / 2 , y_ + m2 / 2);
        double m3 = h * g(x_ + k2 / 2 , y_ + m2 / 2);

        double k4 = h * f(x_ + k3 , y_ + m3);
        double m4 = h * g(x_ + k3 , y_ + m3);

        x_ += (k1 + 2 * k2 + 2 * k3 + k4) / 6.0;
        y_ += (m1 + 2 * m2 + 2 * m3 + m4) / 6.0;

        v.push_back(make_pair(t , make_pair(x_ , y_)));
    }
    return v;
}

double f(double x , double y){
    return 2 * x - 0.02 * x * y; // 3*x-y;
}

double g(double x , double y){
    return 0.0002 * x * y - 0.8 * y; // 4*x-y;
}

//
//      {x' = a*x(t) - b*x(t)*y(t)
//      {y' = c*x(t)*y(t) - d*y(t)
//
//      a = 2 ; b = 0.02 ; c = 0.0002 ; d = 0.8
//

//
//      {x' = 3x - y
//      {y' = 4x - y
//
//      x(0) = 5 ; y(0) = 8
//
//      {x = (5 + 2t)e^t
//      {y = (8 + 4t)e^t
//

int main(int argc, _TCHAR* argv[]){
    cyrillic;
    cout.setf(ios::fixed);
    cout.precision(5);
    double t;
    cin >> t;
    double x = 5000;// 5 //жертви
    double y = 100;// 8 //хижаки

    int n = 1000;

    vector<pair<double , pair<double , double> > > v = Runge_Kutta4(x , y , n , t);

    FILE * file1 = fopen(&path1[0] , "w");
    FILE * file2 = fopen(&path2[0] , "w");

    pair<double , double> mx1 , mx2;
    mx1 = mx2 = make_pair(DBL_MAX , DBL_MIN);

    for(int i = 0 ; i < v.size() ; ++i){
        fprintf(file1 , "  %lf   %lf\n" , v[i].first , v[i].second.first);
        fprintf(file2 , "  %lf   %lf\n" , v[i].first , v[i].second.second);

        mx1.first = min(mx1.first , v[i].second.first);
        mx1.second = max(mx1.second , v[i].second.first);

        mx2.first = min(mx2.first , v[i].second.second);
        mx2.second = max(mx2.second , v[i].second.second);
    }

    fclose(file1);
    fclose(file2);

    Gnuplot gnu("lines");

    gnu.set_grid();

    string aa = "";
    aa += "set yrange [" + dtos(mx1.first - 50) + ":" + dtos(mx1.second + 50) + "]\n";
    aa += "set y2range [" + dtos(mx2.first - 50) + ":" + dtos(mx2.second + 50) + "]\n";
    aa += "set xrange [0:" + dtos(t) + "]\n";
    aa += "set y2tics\n";
    aa += "set ylabel \"Жертви \"\n";
    aa += "set y2label \"Хижаки \"\n";
    aa += "Жертви = '" + path1 + "'\n";
    aa += "Хижаки = '" + path2 + "'\n";
    string bb = "plot Жертви axes x1y1 with lines , Хижаки axes x1y2 with lines";

    gnu.plot_points(bb , aa);

    wait();

    remove(&path1[0]);
    remove(&path2[0]);

    gnu.remove_tmpfiles();

    system("pause");
    return 0;
}