function [x,y]=Euler_b(ydot_fun,x0,y0,h,N)
x=zeros(1,N+1);y=zeros(1,N+1);
x(1)=x0;y(1)=y0;
for n=1:N
    x(n+1)=x(n)+h;
    z0=y(n)+h*feval(ydot_fun,x(n),y(n));
    for k=1:3
    z1=y(n)+h*feval(ydot_fun,x(n+1),z0);
    if abs(z1-z0)<1e-3
        break;
    end
    z0=z1;
end
y(n+1)=z1;
end