A convex function is a real-valued function defined on an interval with the property that its epigraph (the set of points on or above the graph of the function) is a convex set.
A rectifier is a electrical device that converts alternating current to direct current, a process known as rectification. Rectifiers are used as components of power supplies and as detectors of radio signals. Rectifiers may be made of solid state diodes, vacuum tube diodes, mercury arc valves, and other technologies.
An SCR is a short form for Silicon Controlled Rectifier, Which is a three terminal semiconductor device. This device is used for rectification, regulation and inversion etc. It is also used as a controlled switch in high rating instruments. That is why this device has such importance.