They are also discrete, coming from a finite set. I remember at the undergrad differential equation class the teacher asked for some arbitrary coefficients so w

They are also discrete, coming from a finite set. I remember at the undergrad differential equation class the teacher asked for some arbitrary coefficients so we can classify the result. She was very surprised that 3 differential equations she got all turned out to be parabolical, which form a set of probability 0 in the full space. But of course the probabilities for equations with small integer coefficients (which is what people wrote) are totally different.