An air-fuel ratio control system of a multi-cylinder internal combustion engine provided with a throttle valve and opening characteristic control means, which system performs feedback control of an air-fuel ratio based on an output of a sensor detecting an air-fuel ratio of exhaust gas and is capable of performing more accurate air-fuel ratio control, is provided. A scratch polynomial having a degree is obtained using an inversionless Berlekamp-Massey process. An embodiment includes determining a pulse width for a first pulse and measuring the width of a second pulse, wherein the second pulse occurs directly after the first pulse. The extinguishing agent is variably and selectively discharged according to the origin and progression of the fire while simultaneously minimizing the water consumption, decreasing the damage caused by water in the case of a fire, and increasing the economic efficiency. In the present invention, dot-shaped diode cathode regions on the back side of the device chip are distributed into the shape of a substantially uniform XY lattice and at the same time, the lattice constant in a Y direction is made longer than that in an X direction in parallel with a linear gate electrode in a reverse conducting IGBT having a large number of the linear gate electrodes.