Rate of Convergence: Definition, Calculus & Examples

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Discussion Overview

The discussion revolves around the concept of the rate of convergence for functions, particularly focusing on the natural logarithm function, ln(x), as it approaches infinity. Participants explore definitions, examples, and the applicability of the rate of convergence in the context of functions versus sequences.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant seeks a general definition of the rate of convergence for functions, noting that existing resources primarily address sequences.
  • Another participant questions what the function is expected to converge to, suggesting that the inquiry may be about the convergence of a sequence approximating the function.
  • A specific example is provided regarding the rate of convergence of ln(x) as x approaches infinity.
  • Concerns are raised about the limit of ln(x) as x approaches infinity, with a participant clarifying that it diverges to infinity, thus questioning the relevance of discussing its rate of convergence.
  • One participant expresses a desire to understand the 'velocity' with which ln(x) approaches its limit, referencing a Wikipedia article that discusses rates of convergence for sequences.
  • There is a clarification that ln(x) is a function and not a convergent series, with emphasis on the limited convergence of its Taylor series expansion.
  • A participant acknowledges that ln(x) converges to infinity at a slow rate and seeks a method analogous to the rate of convergence for functions.
  • Discussion includes the derivative of ln(x) and its implications for understanding the function's behavior as x approaches infinity.

Areas of Agreement / Disagreement

Participants generally agree on the distinction between functions and sequences regarding convergence. However, there is no consensus on how to define or calculate the rate of convergence for functions, particularly ln(x), as multiple interpretations and approaches are presented.

Contextual Notes

Participants express uncertainty regarding the applicability of the rate of convergence concept to functions, particularly in the case of ln(x), which diverges as x approaches infinity. The discussion highlights the limitations of existing definitions and the need for clarification on the topic.

petermer
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Hi to all! I'm new to calculus and would like to know how to find the rate of convergence for a function. I'm aware of the Wikipedia article, but it only defines it for a sequence. So, what is the general definition?
 
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what are you hoping your function converges on?

i would have imagined you are trying to find the rate of convergence of a sequence approximating the function.
 
For example, I'd like to find the rate of convergence of lnx as it approaches infinity.
 
as you sure you're not trying to find the limit of ln(x) as x approaces infinity?

the limit as x goes to infinity of ln(x) is infinity. what are you hoping ln(x) converges on?

if you're talking about the rate of convergence of the taylor series expansion of ln(x), the series only converges in the range -1 <= x < 1. it diverges outside this range so makes not sense to test the rate of convergence of it as x goes to infinity.

to be honest, i don't understand what you are asking.
 
I do know it's limit, but I'm trying to find the rate (name it 'velocity') with which this function converges to it's limit, infinity. I'm referring to http://en.wikipedia.org/wiki/Rate_of_convergence" Wikipedia article. There, for example, it is mentioned that the sequence 1/2^x converges to it's limit to infinity, 0, with a rate of 1/2. I just look for a more generalized version of this method.
 
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from your wiki link, the speed at which a convergent sequence approaches its limit is called the rate of convergence...

ln(x) isn't a convergent series, it's a function.

and as mentioned before, the series expansion for ln(x) only converges for a small range of x.
 
Ok, I certainly agree with that. But it is a fact that the function lnx is a very slow function, meaning it converges to infinity (as x goes to infinity) with a very slow rate. I understand that I do not have a series here, but would like to know if there is a similar method to the rate of convergence for functions.
 
well if y = \ln x, then i guess that dy/dx = 1/x so evaluting the limit of this would give 0... which makes sense if you interpret what \ln x looks like graphically.

as expected, the rate of change of the function would slow down to a point where it's basically not changing as x goes to infinity.
 

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