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

• 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

Information theory and mathematics

• Entropy (information theory), also called Shannon entropy, a measure of the unpredictability or information content of a message source
• 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)

Other uses in science and technology

• 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

Media

Software

• Entropy (package manager), a Sabayon Linux package manager
• Entropy (anonymous data store), a discontinued project to build a computer network designed to be resistant to censorship