Quadratic exponential sum
= Quadratic exponential sum
{title2=$\sum_{n=1}^N e(\alpha n^2+\beta n)$}
A quadratic exponential sum has a polynomial phase of degree two. Its multiplicative derivative at lag $h$ has the <linear phase> $2\alpha hn$ up to a constant factor. This degree reduction lets the <Van der Corput inequality for finite scalar sequences> reduce its size to estimates for <finite geometric series>.