Is the Inner Product Space in C[0,2] Satisfied by the Integral Equality?

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Discussion Overview

The discussion revolves around the properties of the inner product space in C[0,2], specifically examining the validity of an inequality involving the integral of continuous functions. Participants explore the implications of the inner product defined as the integral of the product of functions and seek to demonstrate a relationship between the norm of a function and the magnitude of its integral.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant defines the inner product in C[0,2] as = the integral of f(t)g(t)* from 0 to 2 and poses a question regarding the inequality involving the norm of f.
  • Another participant seeks clarification on the notation g* and is informed that it refers to the conjugate.
  • A participant reiterates the inner product definition and suggests considering the Cauchy–Schwarz inequality as a potential tool for proving the inequality.
  • One participant expresses skepticism about the relevance of the Cauchy–Schwarz inequality, stating their focus is on f rather than g.
  • A later reply presents a mathematical derivation attempting to show the inequality holds, including clarifications on notation and calculations involving averages and norms.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the applicability of the Cauchy–Schwarz inequality, with some supporting its use while others question its relevance. The discussion remains unresolved regarding the proof of the proposed inequality.

Contextual Notes

There are limitations in the discussion, including potential missing assumptions regarding the functions involved and the dependence on the definitions of the inner product and norm. The relevance of the Cauchy–Schwarz inequality is also contested.

Poirot1
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consider C[0,2], the set of continuous functions from [0,2] to C.

The inner product is <f,g> = the integral of f(t)g(t)* from 0 to 2. show that:

sqrt(2)||f|| is greater than or equal to the magnitude of the integral of f from 0 to 2, where ||.|| is the norm of f.
 
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What does g* mean?
 
conjugate
 
Poirot said:
consider C[0,2], the set of continuous functions from [0,2] to C.

The inner product is <f,g> = the integral of f(t)g(t)* from 0 to 2. show that:

sqrt(2)||f|| is greater than or equal to the magnitude of the integral of f from 0 to 2, where ||.|| is the norm of f.
What have you tried so far? Can you think of results that might help here (Cauchy–Schwarz inequality perhaps, for a suitable choice of g)?
 
Opalg said:
What have you tried so far? Can you think of results that might help here (Cauchy–Schwarz inequality perhaps, for a suitable choice of g)?

I've tried writing what each side is. I don't see how schwarz inequality is relevant. I'm interested in f, not g.
 
$$|\int_0^2 f(t)dt|=|2\bar{f}_1+2i\bar{f}_2|=\sqrt{4(\bar{f}_1)^2+4(\bar{f}_2)^2}=2\sqrt{(|\bar{f}|)^2}\leq 2\sqrt{\bar{|f|^2}}=2\sqrt{(\int_0^2 |f|^2 dt)/2}=\sqrt{2}||f||$$

where the bar is the average and $$f=f_1+if_2$$.

EDIT: I made a correction and some clarifications of notation.
 
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