As most of the operation you perform don't work for most shapes of input data, I'm assuming you're calling this code with scalars.
What happens when you plot a line with a single point? You don't get a line. If you want to see a point, you need to change the default.
function V_Gauss_Pulse(t, to, t_w)
tp = (t-to).^2./t_w.^2;
vg = exp(tp);
plot(vg,t,'*')
end
