function [t,y] = euler(n,dt,u,y1)
    y=zeros(n,dt);
    t=zeros(n,dt);
    y(1)=y1;

    for i=1:(n.dt)
        y(i+1) = y(i) + dt * (-3*y(i) - 1 + u);
        t(i+1) = t(i) + dt;
    end
end