What Does It Mean for a Function to Be Single Valued?

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Discussion Overview

The discussion centers around the concept of single-valued functions in the context of Fourier Series and the Dirichlet conditions. Participants explore the definition of single-valued functions and provide examples to illustrate their points.

Discussion Character

  • Conceptual clarification, Debate/contested

Main Points Raised

  • One participant defines a single-valued function as one where for each input x, there is only one output y.
  • Another participant cites the square root function as an example of a double-valued function, suggesting it does not meet the single-valued criterion.
  • A subsequent reply challenges the classification of the square root function, arguing that it is defined to be always positive for positive real numbers, thus making it single-valued in that context.
  • Further clarification is made regarding the distinction between the definition of the square root function and the solutions to equations involving square roots, highlighting that the latter can yield multiple values.
  • One participant uses an analogy to emphasize the difference between multivalued functions and single-valued functions.

Areas of Agreement / Disagreement

Participants express disagreement regarding the classification of the square root function, with some asserting it is double-valued while others argue it is single-valued based on its definition.

Contextual Notes

The discussion reflects varying interpretations of the term "single-valued" and the implications of function definitions in mathematical contexts. There are unresolved nuances regarding the definitions and examples provided.

Hermes10
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Hello,

I was doing problem involving Fourier Series and came across the Dirichlet conditions which say among others that the function has to be single valued in order to be able to use Fourier Series to describe it.

What does it mean for a function to be single valued?


Hermes10
 
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It means what it says. y=f(x) is single-valued if given an x, there is only one y.

An example which is not is f(x) = square root of x, which is double valued.
 
mathman said:
An example which is not is f(x) = square root of x, which is double valued.
This isn't true. The square root function of a positive real number is defined to be always positive.

This is different from solving equations involving square roots. For example, if x2 = 4, then there are two solutions: √4 = 2, or -√4 = -2.
 
eumyang said:
This isn't true. The square root function of a positive real number is defined to be always positive.

This is different from solving equations involving square roots. For example, if x2 = 4, then there are two solutions: √4 = 2, or -√4 = -2.

Nitpicker!
 
"Multivalued functions" are to "functions" as "counterfeit money" is to "money".
 

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