Inequality on $\ell_p$: Proving or Disproving?

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Discussion Overview

The discussion revolves around the inequality ||x||_{p} ≤ ||x||_{p'} for all x ∈ ℝⁿ when p' > p ≥ 1. Participants are exploring whether this inequality can be proven or disproven, with a focus on its implications and related inequalities.

Discussion Character

  • Exploratory
  • Mathematical reasoning

Main Points Raised

  • One participant asks for a proof or disproof of the inequality ||x||_{p} ≤ ||x||_{p'} for p' > p ≥ 1, clarifying that it is not a homework problem.
  • Another participant expresses curiosity about the inequality, noting that ||x||_{m} ≤ ||x||_{1} holds for any positive integer m, and questions if a similar statement is true for any p ≥ 1.
  • A different participant attempts to provide a reasoning approach by stating that ||x||^p_p = ∑_i{|x_i|^p} ≤ (∑_i{|x_i|})^p = ||x||_1^p, referencing a known inequality involving sums.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the validity of the inequality ||x||_{p} ≤ ||x||_{p'} for p' > p ≥ 1, and multiple viewpoints and approaches are presented without resolution.

Contextual Notes

Some assumptions and dependencies on definitions are not fully explored, and the mathematical steps leading to the proposed inequality remain unresolved.

forumfann
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Could anyone prove or disprove the following inequality:
[itex]||x||_{p}\leq||x||_{p'}[/itex] for all [itex]x\in\mathbb{R}^{n}[/itex] if [itex]p'>p\geq1[/itex]?

By the way, this is not a homework problem.

Any help on this will be highly appreciated.
 
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forumfann said:
Could anyone prove or disprove the following inequality:
[itex]||x||_{p}\leq||x||_{p'}[/itex] for all [itex]x\in\mathbb{R}^{n}[/itex] if [itex]p'>p\geq1[/itex]?

By the way, this is not a homework problem.

Any help on this will be highly appreciated.

Where is the problem from?
 
This a problem that I was curious about, because we know that [itex]||x||_{m}\leq||x||_{1}[/itex] for any positive integer [itex]m[/itex], and then I wondered if it is true for any [itex]p\geq1[/itex].

But it would be great if one can show the following:
[itex]||x||_{p}\leq||x||_{1}[/itex] for [itex]p\geq1[/itex],
so could anyone help me on this?
 
Last edited:
[tex]\|x\|^p_p = \sum_i{|x_i|^p} \leq \left( \sum_i{(|x_i|)} \right)^p = \|x\|_1^p[/tex]

Though I am very dizzy right now, it should be OK where I used [itex]a^2+b^2 \leq (a+b)^2, a,b > 0[/itex]
 

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