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  2. Non-linear sigma model - Wikipedia

    en.wikipedia.org/wiki/Non-linear_sigma_model

    In quantum field theory, a nonlinear σ model describes a field Σ which takes on values in a nonlinear manifold called the target manifold T.The non-linear σ-model was introduced by Gell-Mann & Lévy (1960, section 6), who named it after a field corresponding to a spinless meson called σ in their model. [1]

  3. 68–95–99.7 rule - Wikipedia

    en.wikipedia.org/wiki/68–95–99.7_rule

    Diagram showing the cumulative distribution function for the normal distribution with mean (μ) 0 and variance (σ 2) 1. These numerical values "68%, 95%, 99.7%" come from the cumulative distribution function of the normal distribution. The prediction interval for any standard score z corresponds numerically to (1 − (1 − Φ μ,σ 2 (z)) · 2).

  4. Sigma bond - Wikipedia

    en.wikipedia.org/wiki/Sigma_bond

    According to the sigma bond rule, the number of sigma bonds in a molecule is equivalent to the number of atoms plus the number of rings minus one. N σ = N atoms + N rings − 1 This rule is a special-case application of the Euler characteristic of the graph which represents the molecule.

  5. Sigma model - Wikipedia

    en.wikipedia.org/wiki/Sigma_model

    In physics, a sigma model is a field theory that describes the field as a point particle confined to move on a fixed manifold. This manifold can be taken to be any Riemannian manifold , although it is most commonly taken to be either a Lie group or a symmetric space .

  6. Normal distribution - Wikipedia

    en.wikipedia.org/wiki/Normal_distribution

    The standard deviation of the distribution is (sigma). A random variable with a Gaussian distribution is said to be normally distributed , and is called a normal deviate . Normal distributions are important in statistics and are often used in the natural and social sciences to represent real-valued random variables whose distributions are not ...

  7. Sigmoid function - Wikipedia

    en.wikipedia.org/wiki/Sigmoid_function

    Step function – Linear combination of indicator functions of real intervals; Sign function – Mathematical function returning -1, 0 or 1; Heaviside step function – Indicator function of positive numbers

  8. Standard deviation - Wikipedia

    en.wikipedia.org/wiki/Standard_deviation

    A five-sigma level translates to one chance in 3.5 million that a random fluctuation would yield the result. This level of certainty was required in order to assert that a particle consistent with the Higgs boson had been discovered in two independent experiments at CERN , [ 11 ] also leading to the declaration of the first observation of ...

  9. σ-algebra - Wikipedia

    en.wikipedia.org/wiki/Σ-algebra

    In mathematical analysis and in probability theory, a σ-algebra ("sigma algebra"; also σ-field, where the σ comes from the German "Summe" [1]) on a set X is a nonempty collection Σ of subsets of X closed under complement, countable unions, and countable intersections. The ordered pair (,) is called a measurable space.