function [y,t] = euler(yz, y0, t0, dt, steps)
ys = [y0];
ts = [t0];
u1 = yz+1;
u2 = yz-1;
u = u1;
for i=2:steps
    ts(i) = ts(i-1)+dt;
    if (yz-ys(i-1))>0
        u=u1;
    else
        u=u2;
    end
   ys(i)=ys(i-1)+dt*(3*u-3*ys(i-1));
   end
   y=ys;
   t=ts;
   endfunction

[y,t] = euler(20, 0, 0, 0.1, 50);
plot(t,y)