Math 2.0

Functional analysis Definition

Norm induced by an inner product

Builds on Inner product spaceNorm

Definition

Let VV be an inner product space over ℝ\R or ℂ\C, with inner product ⟨⋅,⋅⟩\langle \cdot, \cdot \rangle. The norm induced by the inner product is the map ∥x∥=⟨x,x⟩(x∈V).\norm{x} = \sqrt{\langle x, x \rangle} \qquad (x \in V).

Remarks

It is a norm; the triangle inequality follows from the Cauchy–Schwarz inequality. For the dot product on ℝn\R^n, it is the Euclidean length x12+⋯+xn2\sqrt{x_1^2 + \cdots + x_n^2}. It satisfies the parallelogram law, and the polarisation identity recovers the inner product from it.

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  1. Vector space definition
  2. Inner product definition
  3. Norm definition
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Where this leads

46 pages build on this one.

Further reading

  1. Web https://en.wikipedia.org/wiki/Inner_product_space, Norm properties
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