File:Simple jump in slow-fast systems.svg

import graph;
import math;
import metapost;
 
size(8 inches);
defaultpen(0.45mm);
 
path phasecurve(pair v(pair z), pair z0, real T, real step=0.01, real MAX=3)
{
	real direction=(T>0?1:-1);
	real t;
	T=abs(T);
	path ret=z0;
	pair cur_z=z0;
	for(t=0;t<T;t+=step)
	{
		cur_z=cur_z+v(cur_z)*step*direction;
		if(abs(cur_z.x)>MAX || abs(cur_z.y)>MAX)
		{
			return ret;
		}
		ret=ret..cur_z;
	}
	return ret;
}
 
pair slowfast(pair z)
{
	real eps=0.1;
	return (eps,-(z.y*z.y+z.x-2));
}
 
path boundary=(-3,-3)--(3,-3)--(3,3)--(-3,3)--cycle;
draw(boundary);
pair[] inits={
	(-2,3), (-1,3), (0,3), (1,3), (2,3), (2.5, 3),
	(-2,-1),(-1,-1),(0,-1),(1,-1),(1,-0.8),
	(-2,-2.1),(-1,-2),(0,-1.7),(1.5,-0.5),(1.7,-0.6)
};
for (pair init: inits)
{
	draw(phasecurve(slowfast,init,15),Arrow(4mm, Relative(0.3)));
}
 
draw(firstcut(graph(new pair(real t){return (2-t*t,t);},-3,0),boundary).after, p=rgb(1,0.0,0.0));
draw(lastcut (graph(new pair(real t){return (2-t*t,t);}, 0,3),boundary).before,p=rgb(0.2,0.8,0.2));
 
xaxis("${y}$",BottomTop,p=fontsize(30),EndArrow);
yaxis("${x}$",LeftRight,p=fontsize(30),EndArrow);