2.4.m

利用龙格库塔法（等步长

t0=0;
tend=10;
A=[-4,0.2;-4,0.6;-4,1.0;-4,1.6]'
for j=1:4
    u0=A(:,j);
    N=1000;
    h=(tend-t0)/N;
    result=[u0'];
    time=[t0];
    u=u0;
    t=t0;
    for k=1:N
        k1=fvdp2(t,u);
        k2=fvdp2(t+h,u+h*k1);
        k3=fvdp2(t+h/2,u+h*k1/4+h*k2/4);
        u=u+h*(k1+k2+4*k3)/6;
        t=t+h;
        result=[result;u'];
        time=[time;t];
        plot(result(:,1),result(:,2))
        hold on
    end

end