function x=ruku(xo,to,t,N);

dt=(t-to)/N
x(1,1:length(xo))=xo
for i=2:N+1
    a=x(i-1,:)
    k1=dt*F1(a);
    k2=dt*F1(a+k1/2);
    k3=dt*F1(a+k2/2);
    k4=dt*F1(a+k3);
    x(i,:)=a+(k1+2*k2+2*k3+k4)/6;
end