Question

how to obtain describing function for on off non linearity

Answer 1

us recall the basic definition of linear system. Linear systems are those where principle of superposition (if the two inputs are applied simultaneously, then output will be the sum of two outputs) is applicable but in case of highly non linear system we cannot apply principle of superposition. Analysis of different non linear system is very difficult because of non linear behavior. Also we cannot use pole zero method in order to analyse non linear systems because pole zero method is strictly restricted to linear systems. Instead of these disadvantages, there are some advantages of having non linear systems and they are written below: