La memoria della materia, la materia della memoria

The first part of the paper is devoted to the analysis of dynamical systems performance. Specifically, in these systems the effects of past inputs on the present state may be regarded as a form of memory (whereas a static system can be considered as memoryless). The second part of the paper describes the standard storage devices adopted in the field of computer technology as well as other storing devices for recording words, sounds and images

PECULIAR CHARACTERISTICS OF STABILITY REGIONS FOR A CLASS OF DIGITAL FILTERS WITH QUANTIZATION NONLINEARITIES

Second-order direct-form fixed-point digital filters with two value truncation quantizers are considered. A brief review of previous results concerning the filter stability and the existence areas of limit cycles in the parameter plane is given. The analysis is extended to almost all regions not previously studied, and some interesting properties of the filter behavior are observed

Modeling frequency responses by positive rational functions

The problem of finding a rational function of a real variable interpolating at given points (with suitable intersection numbers) while being everywhere positive is considered. The positivity requirement is essential, e.g., in modeling the square magnitude of a frequency response. This goal is achieved by resorting to a Hermite-type approach which allows one to obtain positive interpolating functions of minimum complexity by means of an efficient numerical procedure

Approximating delay elements via feedback

A procedure for obtaining a proper rational approximant of the transfer function of a delayer is suggested. In particular, the step response of the unity-feedback system with the delayer in the direct path is first approximated by truncating the Fourier series expansion of its periodic component, and then the corresponding direct-path rational transfer function is derived, thus arriving at a stable Blaschke produc

The Hurwitz matrix and the computation of second-order information indices

International Series of Numerical Mathematics, vol. 12