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  2. Absolute value - Wikipedia

    en.wikipedia.org/wiki/Absolute_value

    The four fundamental properties of the absolute value for real numbers can be used to generalise the notion of absolute value to an arbitrary field, as follows. A real-valued function v on a field F is called an absolute value (also a modulus, magnitude, value, or valuation) [17] if it satisfies the following four axioms:

  3. Ostrowski's theorem - Wikipedia

    en.wikipedia.org/wiki/Ostrowski's_theorem

    The real absolute value on the rationals ... The following proof follows the one of Theorem 10.1 in Schikhof (2007). ... and the multiplicativity property of the ...

  4. Archimedean property - Wikipedia

    en.wikipedia.org/wiki/Archimedean_property

    The field of the rational numbers endowed with the p-adic metric and the p-adic number fields which are the completions, do not have the Archimedean property as fields with absolute values. All Archimedean valued fields are isometrically isomorphic to a subfield of the complex numbers with a power of the usual absolute value. [6]

  5. Absolute value (algebra) - Wikipedia

    en.wikipedia.org/wiki/Absolute_value_(algebra)

    The standard absolute value on the integers. The standard absolute value on the complex numbers.; The p-adic absolute value on the rational numbers.; If R is the field of rational functions over a field F and () is a fixed irreducible polynomial over F, then the following defines an absolute value on R: for () in R define | | to be , where () = () and ((), ()) = = ((), ()).

  6. Triangle inequality - Wikipedia

    en.wikipedia.org/wiki/Triangle_inequality

    The triangle inequality is a defining property of norms and measures of distance. This property must be established as a theorem for any function proposed for such purposes for each particular space: for example, spaces such as the real numbers, Euclidean spaces, the L p spaces (p ≥ 1), and inner product spaces.

  7. Sign function - Wikipedia

    en.wikipedia.org/wiki/Sign_function

    A subderivative value 0 occurs here because the absolute value function is at a minimum. The full family of valid subderivatives at zero constitutes the subdifferential interval [ − 1 , 1 ] {\displaystyle [-1,1]} , which might be thought of informally as "filling in" the graph of the sign function with a vertical line through the origin ...

  8. Geometrical properties of polynomial roots - Wikipedia

    en.wikipedia.org/wiki/Geometrical_properties_of...

    Landau's inequality provides an upper bound for the absolute values of the product of the roots that have an absolute value greater than one. This inequality, discovered in 1905 by Edmund Landau , [ 9 ] has been forgotten and rediscovered at least three times during the 20th century.

  9. Proofs involving ordinary least squares - Wikipedia

    en.wikipedia.org/wiki/Proofs_involving_ordinary...

    The normal equations can be derived directly from a matrix representation of the problem as follows. The objective is to minimize = ‖ ‖ = () = +.Here () = has the dimension 1x1 (the number of columns of ), so it is a scalar and equal to its own transpose, hence = and the quantity to minimize becomes