Can different weights help determine the difference between two functions?

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Discussion Overview

The discussion revolves around methods for quantifying the difference between two functions, particularly through mathematical techniques such as integrals and inner products. Participants explore various approaches and the implications of using weighted functions in this context.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant suggests using the integral ##\int_\Omega (f-g)^2 \, dx## as a measure of how different two functions are.
  • Another participant notes that this approach is a specific case of defining an inner product in a function space and discusses the concept of using a positive weight function in the inner product.
  • A later post questions whether the difference function with a weight of 1 is an adequate representation of distance or if alternative methods might be preferable.
  • It is mentioned that the choice of weights may depend on the specific requirements of the problem being addressed.

Areas of Agreement / Disagreement

Participants express differing views on the appropriateness of using a weight of 1 versus other potential weighting methods, indicating that the discussion remains unresolved regarding the best approach to measure function differences.

Contextual Notes

The discussion does not clarify the specific contexts or applications for which the proposed methods might be most suitable, nor does it resolve the implications of using different weights in the integral.

member 428835
Hi PF!

Can any of you help me determine a good measure for how "different" two functions are from each other?

I've thought of using something like ##\int_\Omega (f-g)^2 \, dx##. Can anyone recommend a good technique and direct me to the theory so I can understand it well?

Thanks so much!

Josh
 
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Your proposal is an option and is a special case of using an inner product for the purpose. You can view the function space as a linear vector space and generally define an inner product by integrating the product of the functions, possibly together with a positive weight function. Your proposal would be equivalent to taking the inner product of the difference function with itself, much like you could determine the distance between two points in any vector space with an inner product.
 
So does this difference function (with weight 1) seem like a good representation for distance, or is there a better method in your opinion?
 
This would depend on exactly what you are looking to do. For some problems, it is natural to use different weights.
 

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