1. A simulation method for a computing system including one or more processors, the simulation method comprising: performing a main simulation as one of a first simulation and a second simulation based on an input deviation, wherein the input deviation is a distribution of a characteristic of a design of an electric circuit; in a case where a function value for a nominal point of the input deviation is a first value, providing a zero point (ZP) for the input deviation to the main simulation, and the main simulation perfoiming the first simulation in response thereto; and in a case where the function value for the nominal point of the input deviation is a second value that is different than the first value, performing a worst case point (WCP) determination for the input deviation by repeatedly performing generating samples of an input within a set boundary of the input deviation while shifting a boundary of the input deviation by reducing the input deviation until the input deviation reaches a minimum critical value, providing the determined worst case point (WCP) value to the main simulation, and the main simulation performing the second simulation in response thereto, wherein the input is the characteristic of the design of the electric circuit.