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Norm (mathematics)




A simple example is the 2-dimensional Euclidean Space R2 equipped with the Euclidean Norm . Elements in this vector space (e.g., (3, 7) ) are usually drawn as arrows in a 2-dimensional Cartesian Coordinate System starting at the origin (0, 0). The Euclidean norm assigns to each vector the length of its arrow.

A vector space with a norm is called a Normed Vector Space . Similarly, a vector space with a seminorm is called a Seminormed Vector Space .


DEFINITION

Given a Vector Space ''V'' over a Subfield F of the Complex Number s such as the complex numbers themselves or the Real or Rational Number s, a '''seminorm on''' ''V'' is a Function ''p'':''V''→'''R'''; ''x''→ ''p''(''x'') with the following properties:

For all ''a'' in ''F'' and all u and '''v''' in ''V'',
  Although Every Vector Space Is Seminormed (eg, With The Trivial Seminorm In The Examples Section Below), It May Not Be Normed Every Vector Space ''V'' With Seminorm ''p''('''v''') Induces A Normed Space ''V/W'', Called The "http://wwwinformationdelightinfo/information/entry/quotient_space" class="copylinks">Quotient Space , where ''W'' is the subspace of ''V'' consisting of all vectors '''v''' in ''V'' with ''p''('''v''') = 0 The induced norm on ''V/W'' is given by ''W''+'''v''' = ''p''('''v''') and is clearly well-defined
  Every "http://wwwinformationdelightinfo/information/entry/linear_form" class="copylinks">Linear Form ''f'' on a vector space defines a seminorm by '''x''' → ''f''('''x''')
  :<math>\\mathbf{x}\ : \sqrt{x_1^2 + \cdots + x_n^2}</math>
  :<math>\\mathbf{z}\ : \sqrt{z_1^2 + \cdots + z_n^2}</math>, equivalent with the Euclidean norm on '''R'''<sup>2''n''</sup>
  :<math>\x\ : 2x_1 + \sqrt{3x_2^2 + \max(x_3,2x_4)^2}</math>
  :<math> \x\ P \left(\sum_{i\in\mathbb N}x_i^p ight)^{ rac1p} </math> resp <math> \f\_{p,X} = \left(\int_Xf(x)^p\,\mathrm dx ight)^{ rac1p} </math>
  Any "http://wwwinformationdelightinfo/information/entry/inner_product" class="copylinks">Inner Product induces in a natural way the norm <math>\x\ := \sqrt{\langle x,x angle}</math>
  :<math>x^ Op Y\le\ X\ P\y\ Q\qquad Rac{1}{p}+ Rac{1}{q} 1</math>1