A set that is not convex is called a non-convex set. A polygon that is not a convex polygon is sometimes called a concave polygon, and some sources more generally use the term concave set to mean a non-convex set, but most authorities prohibit this usage.
In either case you don't need to deal with the absolute value. A rectified sine wave is a periodic signal with a period equal to half of the full sinusoid, I would write the sine in exponential form and integrate over one period to find the series coefficients.
F Ï=Ï (2.2) and the spectrum of a continuous sinusoidal signal is an impulse Î´(Ï), the resultant. convolution is just the Sync function. It can be seen from the equation for the Sync function that as the duration of the. signal decreases, Ïâ0, its spectral width increases until, in the limit, when the. signal can be represented by an impulse Î´(t), the spectral width is infinite. This. relationship is shown graphically in the following figure.