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  2. Digamma function - Wikipedia

    en.wikipedia.org/wiki/Digamma_function

    The only one on the positive real axis is the unique minimum of the real-valued gamma function on R + at x 0 = 1.461 632 144 968 362 341 26.... All others occur single between the poles on the negative axis: x 1 = −0.504 083 008 264 455 409 25... x 2 = −1.573 498 473 162 390 458 77... x 3 = −2.610 720 868 444 144 650 00... x 4 = −3.635 ...

  3. Identity (mathematics) - Wikipedia

    en.wikipedia.org/wiki/Identity_(mathematics)

    Visual proof of the Pythagorean identity: for any angle , the point (,) = (⁡, ⁡) lies on the unit circle, which satisfies the equation + =.Thus, ⁡ + ⁡ =. In mathematics, an identity is an equality relating one mathematical expression A to another mathematical expression B, such that A and B (which might contain some variables) produce the same value for all values of the variables ...

  4. Pfister's sixteen-square identity - Wikipedia

    en.wikipedia.org/wiki/Pfister's_sixteen-square...

    However, the more general Pfister's theorem (1965) shows that if the are rational functions of one set of variables, hence has a denominator, then it is possible for all =. [3] There are also non-bilinear versions of Euler's four-square and Degen's eight-square identities.

  5. Viète's formula - Wikipedia

    en.wikipedia.org/wiki/Viète's_formula

    Viète's formula, as printed in Viète's Variorum de rebus mathematicis responsorum, liber VIII (1593). In mathematics, Viète's formula is the following infinite product of nested radicals representing twice the reciprocal of the mathematical constant π: = + + + It can also be represented as = = ⁡ +.

  6. Vector algebra relations - Wikipedia

    en.wikipedia.org/wiki/Vector_algebra_relations

    The following are important identities in vector algebra.Identities that only involve the magnitude of a vector ‖ ‖ and the dot product (scalar product) of two vectors A·B, apply to vectors in any dimension, while identities that use the cross product (vector product) A×B only apply in three dimensions, since the cross product is only defined there.

  7. Poisson's equation - Wikipedia

    en.wikipedia.org/wiki/Poisson's_equation

    Poisson's equation is an elliptic partial differential equation of broad utility in theoretical physics. For example, the solution to Poisson's equation is the potential field caused by a given electric charge or mass density distribution; with the potential field known, one can then calculate the corresponding electrostatic or gravitational ...

  8. Vector calculus identities - Wikipedia

    en.wikipedia.org/wiki/Vector_calculus_identities

    In Cartesian coordinates, the divergence of a continuously differentiable vector field = + + is the scalar-valued function: ⁡ = = (, , ) (, , ) = + +.. As the name implies, the divergence is a (local) measure of the degree to which vectors in the field diverge.

  9. Pokhozhaev's identity - Wikipedia

    en.wikipedia.org/wiki/Pokhozhaev's_identity

    Pokhozhaev's identity is an integral relation satisfied by stationary localized solutions to a nonlinear Schrödinger equation or nonlinear Klein–Gordon equation. It was obtained by S.I. Pokhozhaev [1] and is similar to the virial theorem. This relation is also known as G.H. Derrick's theorem. Similar identities can be derived for other ...