Question about Elementary Functions

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    Elementary Functions
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Discussion Overview

The discussion revolves around the nature of elementary functions and their integrals, specifically exploring the smallest set of functions that includes elementary functions and is closed under integration. The conversation touches on definitions, examples, and the complexity of integrals related to elementary functions.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • One participant notes that many elementary functions do not have elementary integrals, using the example of the integral of e^-(x^2) as a non-elementary function.
  • Another participant argues that the classification of a function as elementary can depend on the precise definition used, citing the error function erf(x) as an example of a function derived from an integral of an exponential function.
  • A third participant provides a definition of elementary functions, describing them as constructed from exponentials, logarithms, trigonometric functions, constants, and roots of equations through specific operations.
  • One participant expresses uncertainty about the feasibility of describing the integrals of all elementary functions, suggesting that the set of all elementary functions is complex and involves infinite transcendence degree over C(X).

Areas of Agreement / Disagreement

Participants do not reach a consensus on the definition of elementary functions or the nature of their integrals, indicating multiple competing views and unresolved questions.

Contextual Notes

The discussion highlights the dependence on definitions of elementary functions and the complexity involved in their integration, with no resolution on the completeness of the proposed sets.

lugita15
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Obviously, most elementary functions do not have elementary functions as integrals. For instance, the integral of e^-(x^2) is not an elementary function even though its integrand is. My question is, what is the smallest set of functions which includes the set of elementary function and is closed under integration?
 
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To some extent it depends on a precise definition of "elementary function". For example, the integral of e^[(-x^2)/2] (with appropriate normalizations) is called erf(x). Whether or not it is elementary becomes a matter of definition.
 
As to what constitutes an elementary function I define it as follows:
An elementary function is a function built from a finite number of exponentials, logarithms, trigonometric functions, inverse trigonometric functions, constants, one variable, and roots of equations through composition and combinations using the four elementary operations (+ - × ÷). The roots of equations are the functions implicitly defined as solving a polynomial equation with constant coefficients.
 
even the simpler question of describing integrals of all elementary functions seems a tall order. i.e. of giving a collectioncontaining integrals of all elementarty functions and possibly not closed under integration.

i have no idea.

even the set of all elementary functions is a field extension of infinite transcendence degree over C(X) hence more than a bit complicated.
 

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