Variation Question: f Min then \delta f, \delta^2 f?

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Discussion Overview

The discussion revolves around the concept of variation in the context of functions that have a minimum. Participants explore the implications of having a minimum on the variation and derivatives of a function, including the definitions and interpretations of these terms.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • Some participants propose that if a function has a minimum, then the variation of that function, denoted as \(\delta f\), could be zero or greater than zero, while the second variation, \(\delta^2 f\), should be greater than zero.
  • Others express confusion regarding the terminology used, particularly the meaning of "variation" and how it relates to the function's derivatives at a minimum.
  • A participant mentions the total variation of a function on a given interval and questions the specific interval being referenced in the original question.
  • One participant clarifies that they are referring to the infinitesimal change of a function while keeping the argument fixed, defining variation as \(\delta \varphi(x) = \bar{\varphi}(x) - \varphi(x)\).
  • Another participant challenges the clarity of the definition provided, noting that the relationship between \(\bar{\varphi}(x)\) and \(\varphi(x)\) is not specified.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the definitions and implications of variation, with multiple competing views and interpretations remaining unresolved.

Contextual Notes

Limitations include unclear definitions of variation and its relationship to the function, as well as the lack of specified intervals for total variation.

matematikuvol
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If f has minimum, than

[tex]\delta f=0[/tex], [tex]\delta^2 f>0[/tex]

or

[tex]\delta f>0[/tex]?
 
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I think you're going to need to answer your question more clearly. I really am not sure what you're talking about.
 
If some function has minimum. Then variation of that function is equal zero or bigger then zero?
 
Well, what do you mean by "variation" of a function? I know the "total variation of a function" on a given interval. If that is what you mean, what is the interval.

(The derivative, if that might be what you mean, of a function, at a minimum, is 0 and the second derivative either 0 or positive. A simple example is [itex]x^2[/tex] which has a minimum at x= 0. The derivative is 2x which is 0 at x= 0 and the second derivative is 2 which is positive.)[/itex]
 
I mean by variation infinitesimal change of function while argument stay fiksed.

[tex]\varphi(x)[/tex]
[tex]\bar{\varphi}(x)[/tex]

variation

[tex]\delta \varphi(x)=\bar{\varphi}(x)-\varphi(x)[/tex]
 
Which again makes no sense because you don't say how φ¯(x) is related to φ(x).
 

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