Simpson's rule approximates the integrand by a piecewise quadratic function. The integrand simplifies to 1, so the antiderivative is "x". Note that the integrand is the sinc function, and also the zeroth . This formula is sometimes used for numerical computation, since the integrand decreases very quickly. These conventions correspond to interpreting the integrand as a differential form, integrated over a chain. The function to be integrated is called the integrand. To simplify the calculations, one first takes the variation of the square of the integrand. This directly results from the fact that the integrand formula 17 is an even function. Next we seek an upper bound for the integrand when . It is most efficient when the peaks of the integrand are well-localized. Of course the "right" choice strongly depends on the integrand. The symbol is separated from the integrand by a space (as shown).