Entropy (disambiguation)

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Entropy, in thermodynamics, is a state function originally introduced to explain why part of a thermodynamic system's total energy is unavailable to do useful work.

Entropy may also refer to:

Thermodynamics and statistical mechanics[edit]

  • Entropy (classical thermodynamics), thermodynamic entropy in purely macroscopic terms, with less emphasis on the statistical explanation
    • Entropic force. The product of temperature and the gradient of the entropy density is viewed an effective force, yielding a gradient in the energy density of a system.
  • Entropy (statistical thermodynamics), the statistical explanation of thermodynamic entropy based on probability theory
    • Configuration entropy, the entropy change due to a change in the knowledge of the position of particles, rather than their momentum
    • Conformational entropy, the entropy change due to a change in the "configuration" of a particle (e.g. a right-handed vs. a left-handed polyatomic molecule)
  • Tsallis entropy, a generalization of Boltzmann-Gibbs entropy
  • von Neumann entropy, entropy in quantum statistical physics and quantum information science

Introductory articles[edit]

Other aspects[edit]

Information theory and mathematics[edit]

  • Entropy (information theory), also called Shannon entropy, a measure of the unpredictability or information content of a message source
    • Entropy of entanglement, related to the Shannon and von Neumann entropies for entangled systems; reflecting the degree of entanglement of subsystems
  • Algorithmic entropy an (incomputable) measure of the information content of a particular message
  • Rényi entropy, a family of diversity measures generalising Shannon entropy; used to define fractal dimensions
  • Measure theoretic entropy, a measure of exponential growth in dynamical systems; equivalent to the rate of increase of Shannon entropy of a trajectory in trajectory-space
  • Topological entropy, a measure of exponential growth in dynamical systems; equivalent to the rate of increase of α->0 Renyi entropy of a trajectory in trajectory-space.
  • Topological entropy in physics
  • Volume entropy, a Riemannian invariant measuring the exponential rate of volume growth of a Riemannian metric
  • Maximum entropy (disambiguation)
  • Graph entropy, a measure of the information rate achievable by communicating symbols over a channel in which certain pairs of values may be confused.

Other uses in science and technology[edit]

  • Entropy encoding, data compression strategies to produce a code length equal to the entropy of a message
  • Entropy (computing), an indicator of the number of random bits available to seed cryptography systems
  • Entropy (anesthesiology), a measure of a patient's cortical function, based on the mathematical entropy of EEG signals
  • Entropy (ecology), measures of biodiversity in the study of biological ecology, based on Shannon and Rényi entropies
  • Social entropy, a measure of the natural decay within a social system

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