#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include "ps.h"

void plotd1(void);

int main(void)
{   
     init();
     viewport(0.2, 0.2, 0.8, 0.8); 
     xyworld(-0.2, -0.2, 1.2, 1.2); 
     line(0.5, 0.0, 0.5, 0.02, 0.0, 2.0, 1);
     line(1.0, 0.0, 1.0, 0.02, 0.0, 2.0, 1);
     line(0.0, 0.5, 0.02, 0.5, 0.0, 2.0, 1);
     line(0.0, 1.0, 0.02, 1.0, 0.0, 2.0, 1);
     arrow(-0.1, 0.0, 1.2, 0.0, 0.02, 0.0, 2.0);
     arrow(0.0, -0.1, 0.0, 1.2, 0.02, 0.0, 2.0);
     textx(1.2,-0.02,1,"x"); 
     textx(0.5,-0.02,3,"0.5");
     textx(1.0,-0.02,3,"1.0");
     texty(-0.02,1.2,1,"y"); 
     texty(0.0,0.5,3,"0.5");
     texty(0.0,1.0,3,"1.0");
     textx(-0.06,-0.02,1,"O");
     plotd1();
     fin();

     return 0;
}

void  plotd1(void)
{ 
      int n,m,ix,iy,it;double dt,dx,dy,ds,x0,y0,x1,y1;

      linewidth(1.0); setgray(0.6); linety(1); 
      m=10; 
      for (ix=0;ix<=m;ix++){ 
       for (iy=0; iy<=m;iy++){ 
         x0=0.0+1.0*(double)ix/(double)m; y0=0.0+1.0*(double)iy/(double)m; 
         dt=0.05; dx=1.0; dy=3.0*x0*y0; ds=sqrt(dx*dx+dy*dy); 
         if(ds!=0.0) { 
           x1=x0+dx/ds*0.05; y1=y0+dy/ds*0.05; arrow(x0,y0,x1,y1,0.01,0.6,1.0); 
           }
        }
      }
       stroke(); newpath(); setgray(0.4); linewidth(1.2); linety(1); 
     n=40; m=1; 
     for(ix=0;ix<=0;ix++){ 
      for(iy=0;iy<=0;iy++){ 
        x0=0.0; y0=0.1; 
        dt=0.0128; 
        plot(x0,y0,3); 
         for(it=1;it<=2*n;it++){ 
          x1= x0+1.0*dt;y1= y0+3.0*x0*y0*dt;
          plot(x1,y1,2);
          x0=x1;y0=y1;
          }
       }
      }
      stroke();
     
      return;
}