Are there other non-integrable functions besides x^x?

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Discussion Overview

The discussion centers on the nature of the function x^x and its lack of an indefinite integral expressible in elementary functions. Participants explore whether there are other functions that share this property, delving into the concept of non-integrable functions and related mathematical tools.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant notes that while the integral of x^x exists, it cannot be expressed in elementary functions, suggesting that numerical methods are necessary for evaluation.
  • Another participant mentions that there are many integrals of this nature, implying a broader class of functions that may not have elementary antiderivatives.
  • A later reply discusses elliptic integrals and suggests that functions of the form √P(x), where P(x) is a polynomial of degree three or higher, may also lack elementary antiderivatives.
  • Participants mention the term "nonelementary function" to describe functions that do not have expressible antiderivatives and note the absence of a clear definition for this term.
  • Suggestions for alternative methods of integration are provided, including numerical analysis and Taylor series expansion, although these methods have limitations.
  • It is stated that if antiderivatives exist but cannot be expressed in elementary terms, the function is still considered integrable.

Areas of Agreement / Disagreement

Participants express differing views on the classification of functions and the nature of integrability, indicating that multiple competing perspectives remain without a clear consensus.

Contextual Notes

The discussion highlights limitations in defining non-integrable functions and the conditions under which certain integrals can be evaluated, particularly regarding the scope of elementary functions.

mahesh_2961
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hai
i heard that the function x^x doesn't have any indefinite integral and hence one can't find definite integral by normal methods .. So one has to go for numerical methods , i haven't tried this ...
just curious to know if there exist more fuctions in the same class ...

regards
mahesh :smile:
 
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Well, the integral "exists" of course, but it's not the expressible in elementary functions.

There are many such integrals of this nature.
 
Thanx wolfe, can u tell me where i can find such functions

Mahesh
 
DeadWolfe said:
Well, the integral "exists" of course, but it's not the expressible in elementary functions.

There are many such integrals of this nature.

Yap,just about elliptic integrals.Basically most of the type [itex]\sqrt{P(x)}[/itex],where P(x) is a polynomial with real coeffcients of degree larger of equal with 3,get the "chance" of not having a "cute" antiderivative.Mathematicians invented the famous syntagma "nonelementary function",referring to this sort of functions which come up when searching for antiderivatives.They couldn't come up with a decent definition for this "nonelementary". :-p

Anyway,when you spot something wrong,i.e.u can't find an antiderivative,try for other tools.Numerical analysis works,but only in the case on definite integral,where the result is a number.Sometimes,u can expand the integrand in Taylor series (though the ray may be small) or express it terms on tabulated "nonelementary functions".The books by Abramowitz & Stegun and Gradsteyn & Rytzhik may turn out to be handy.

Daniel.

PS.If the antiderivatives exist,but cannot be expressed in terms of "elementary" functions,then the function which makes up the integrand is integrable.
 
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