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In mathematics, the discrete-time Fourier transform (DTFT) is a form of Fourier analysis that is applicable to a sequence of discrete values. The DTFT is often used to analyze samples of a continuous function. The term discrete-time refers to the fact that the transform operates on discrete data, often samples whose interval has units of time.
The DFT has many applications, including purely mathematical ones with no physical interpretation. But physically it can be related to signal processing as a discrete version (i.e. samples) of the discrete-time Fourier transform (DTFT), which is a continuous and periodic function. The DFT computes N equally-spaced samples of one cycle of the DTFT.
Time constant. In physics and engineering, the time constant, usually denoted by the Greek letter τ (tau), is the parameter characterizing the response to a step input of a first-order, linear time-invariant (LTI) system. [ 1 ][ note 1 ] The time constant is the main characteristic unit of a first-order LTI system. It gives speed of the response.
Block diagram illustrating the superposition principle and time invariance for a deterministic continuous-time single-input single-output system. The system satisfies the superposition principle and is time-invariant if and only if y 3 (t) = a 1 y 1 (t – t 0) + a 2 y 2 (t – t 0) for all time t, for all real constants a 1, a 2, t 0 and for all inputs x 1 (t), x 2 (t). [1]
Time-invariant system. Block diagram illustrating the time invariance for a deterministic continuous-time single-input single-output system. The system is time-invariant if and only if y2(t) = y1(t – t0) for all time t, for all real constant t0 and for all input x1(t). [1][2][3] Click image to expand it. In control theory, a time-invariant ...
The mathematical theory of stability of motion, founded by A. M. Lyapunov, considerably anticipated the time for its implementation in science and technology. Moreover Lyapunov did not himself make application in this field, his own interest being in the stability of rotating fluid masses with astronomical application.
The Lyapunov equation, named after the Russian mathematician Aleksandr Lyapunov, is a matrix equation used in the stability analysis of linear dynamical systems. [1][2] In particular, the discrete-time Lyapunov equation (also known as Stein equation) for is. where is a Hermitian matrix and is the conjugate transpose of , while the continuous ...
The Hamiltonian is a function used to solve a problem of optimal control for a dynamical system. It can be understood as an instantaneous increment of the Lagrangian expression of the problem that is to be optimized over a certain time period. [1] Inspired by—but distinct from—the Hamiltonian of classical mechanics, the Hamiltonian of ...