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.
A sine wave, which is produced by rotating AC machinery, is the type of wave that is generally provided by the utility company with the help of a generator. The benefits of using a pure sine wave inverter include: 1  All equipment currently on the market is designed for use with sine waves.