What are perpendicular functions and how are they used in function spaces?

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Discussion Overview

The discussion revolves around the concept of perpendicular functions, with a focus on their relationship to orthogonal functions within the context of function spaces. Participants explore definitions, properties, and applications, particularly in relation to inner product spaces and projections of functions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant inquires about the concept of perpendicular functions, linking it to perpendicular tangent lines.
  • Another participant suggests that the term "perpendicular functions" may refer to "orthogonal functions," defining them as functions whose integral product over a domain equals zero.
  • A later reply elaborates that in an inner product space, functions are considered perpendicular if their dot product is zero, drawing a parallel to vectors in Euclidean space.
  • This reply also introduces the concept of an orthonormal basis, explaining that it consists of vectors that are both perpendicular and of unit length, and discusses the projection of functions onto such spaces.
  • The example of projecting the function e^x onto a space generated by {1,x,x^2} is provided, noting that this set is not an orthonormal basis, and mentions the role of perpendicular functions in this process.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the terminology of "perpendicular functions," with some suggesting it may be synonymous with orthogonal functions. The discussion remains open with various interpretations and explanations presented.

Contextual Notes

There are limitations in the definitions provided, particularly regarding the assumptions about the nature of function spaces and the specific conditions under which functions are considered orthogonal or perpendicular.

Silverious
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Does anyone know anything about perpendicular functions? I just kinda stumbled onto it thinking about perpendicular tanget lines. Could anyone shed light on the situation?
 
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I'm not sure what you mean by "perpendicular functions" but you might be thinking about "orthogonal functions." The (overly) simple definition of orthogonal functions is that the integral of their product over a domain is zero.
 
Maybe I should consider it more and post a more detailed question. I'll do that.
 
If the two functions belong to an inner product space, they are perpendicular if their dot product is zero just like how any two vectors are perpendicular if their dot product is zero.

An orthonormal basis is a set of vectors that are all perpendicular and have unit length. In R^3 Euclidean space, (1,0,0), (0,1,0), and (0,0,1) are in such a basis. In a function space, a space with functions in it, you might have a list of orthonomoral functions (which are still vectors). Then you can project another function onto the space using the orthonormal basis. For example, if you project e^x onto the space generated by {1,x,x^2} which BTW is not itself an o.n. basis, then you get a 2nd degree polynomial that approximates e^x. Perpedicular functions run amok in this process. . .
 

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