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.
The left-hand side of the full-wave rectifier circuit consists of four diodes: a diode bridge. Half-wave current is a current that can only flow in alternate current, a full-wave current can flow both alternating current and direct current. rectifier is a device that can convert Alternating current (AC) to Direct current (DC). This is a process called rectification.