humps is a test function for finding zeros, for optimization
and integration. Its root is at x = 1.2995, a (local) minimum
at x = 0.6370, and the integral from 0.5 to 1.0
is 8.0715.

sinc is defined as $sinc(t) = \frac{\sin(\pi t)}{\pi t}$.
It is the continuous inverse Fourier transform of the rectangular pulse
of width $2\pi$ and height $1$.

psinc is the 'periodic sinc function' and is defined as
$psinc(x,n) = \frac{\sin(x n/2)}{n \sin(x/2)}$.