ABSTRACT
It is well known that an investigation of processes and phenomena is linked, –rst of all, with the construction of mathematical models describing these processes and phenomena using mathematical language. The model is characterized by some parameters. These parameters include input variables or control actions as they are called, or simply controls, output variables or output coordinates, or controlled variables, and also intermediate variables, the so-called state variables. In most cases processes are not considered in isolation but in direct connection with other processes and phenomena. The inœuence of external conditions-the environment-is characterized by the so-called disturbing inœuences or, simply, disturbances.
