numerical methods for the system of differential equations

Question

I need to solve this system of differential equations by ballistic method. $$\begin{cases}\dot{w}=-2ew+u; \\\dot{u}=4eu-4(e^2-w^2)w;\end{cases}$$ where $e<0; w(0)=w_{0}(\text{any number}); u(0)=?; $ I have written a program, but I think it doesn't work correct. Here is my code from Matlab:

clear all
e=-1; 
eps = 0:2:10;
N=100;
f=@(z,e)[-2*e*z(1)+z(2); 4*e*z(2)-4*(e^2-z(1)^2)*z(1)];
h=(5)/(N-1);
for l=1:length(eps)
    iter = 0;
    v0=1.4; v1=0.7;
    while (abs(v1-v0))>(e)&(iter<20) 
        v0=v1;
        y(1,1)=0.6; y(2,1)=v0;
        for n=1:(N-1)
            k1=f(y(:,n),eps(l));
            k2=f(y(:,n)+0.5*h*k1,eps(l));
            k3=f(y(:,n)+0.5*h*k2,eps(l));
            k4=f(y(:,n)+0.5*h*k3,eps(l));
            y(:,n+1)=y(:,n)+(h/6)*(k1+2*k2+2*k3+k4);
        end
        v1=v0-(y(1,N)-1)/y(2,N);
        iter=iter+1;
    end
    hold on
    plot(0:h:5,y(1,:));
end

Thank you for the help! Sorry for my English.