function vp = prob3f(t,y,Z,v0,a,b,r,m)
ylag = Z(:,1);
v = y(1);
w = y(2);
vp = zeros(2,1);
vp(1) = v - v^3 / 3 + w  + m * (ylag(1) - v0);
vp(2) = r * (v + a - b*w);