The absolute value function flips the sign of negative numbers, and leaves positive numbers alone. The Heaviside function is very similar; 1 for positive numbers and 0 for negative numbers. By the way, the Heaviside function, rather than being named after its shape, is named after Oliver Heaviside, who was awesome. But that sounds a bit like the delta function; zero everywhere, except for an infinite spike at x=0. Answer Gravy: The Dirac delta function really got under the skin of a lot of mathematicians.