14
$\begingroup$

When teaching integration to beginning calculus students I always tell them that some integrals are "impossible" (with a bit of expansion on what that actually means). However I must admit that the examples I give mostly come from "folklore" or guesswork.

Can anyone point me to a list (not a complete list of course!) of fairly simple elementary functions whose antiderivatives are not elementary? I'm thinking of things like $\exp(x^2)$ which is the standard example, $\sin(\exp(-x))$ perhaps, things like this, not hugely complicated formulae.

$\endgroup$
  • 2
    $\begingroup$ $\displaystyle\int x^{^{\tfrac x{\ln x}}}dx\qquad$ ;-) $\endgroup$ – Lucian Feb 18 '14 at 6:00
  • $\begingroup$ @Lucian, can we say that's a " "non-elementary" " integral? - note the double quotes... ;-) $\endgroup$ – David Feb 18 '14 at 6:04
  • $\begingroup$ It would be nice to have some source which not only gives a list of functions, which are not elementary integrable, but also gives some references pointing to proofs that they are not elementary integrable. That's why I have added a bounty. (But if no such answer appears, I will award bounty to the existing answer, so that the bounty rep is not wasted.) $\endgroup$ – Martin Sleziak Jul 4 '14 at 8:04
14
+50
$\begingroup$

Try this link. A lot of simple functions, btw :)

http://calculus-geometry.hubpages.com/hub/List-of-Functions-You-Cannot-Integrate-No-Antiderivatives


As was said in the comment below, the link doesn't work now.

Still, nothing could be deleted from the Internet permanently.

http://web.archive.org/web/20160612175604/http://hubpages.com:80/education/List-of-Functions-You-Cannot-Integrate-No-Antiderivatives

$\endgroup$
  • $\begingroup$ Thanks @sas, exactly what I wanted. Loved the item on "curious exceptions". $\endgroup$ – David Feb 18 '14 at 6:38
  • $\begingroup$ The link does not work anymore. $\endgroup$ – projectilemotion Jun 13 '17 at 7:35
12
+100
$\begingroup$

Liouville's theorem in fact exactly characterizes functions whose antiderivatives can be expressed in terms of elementary functions.

However, the only proof I have seen is not exactly suitable for teaching beginning calculus students. In fact, the proof of the impossibility of solving a general 5th degree polynomial by radicals (by Galois) and the proof of Liouville's theorem share a common idea. (Liouville's theorem is part of what is called differential Galois theory)

If you are prepared to wade through a bit of differential Galois theory to get to the proof, you could read R.C.Churchill's notes available here.

You could also try Pete Goetz's presentation here which assumes Liouville's theorem and proves the the Gaussian does not have a elementary antiderivative.

Note: Proving that a certain function does not have an elementary antiderivative is often quite difficult, and reduces to the problem of showing that a certain differential equation does not have a solution.

I have not seen many examples of such functions, and I do not know a reference which proves it for all the functions listed in the previous answer by sas.

$\endgroup$
1
$\begingroup$

The reference below treats as example six different classes of simple nonelementary integrals.

Yadav, D. K.: A Study of Indefinite Nonintegrable Functions. PhD thesis, Vinoba Bhave University, India, 2012

Yadav, D. K.: Six Conjectures in Integral Calculus. 2016

Yadav, D. K.: Six Conjectures on Indefinite Nonintegrable Functions or Nonelementary Functions. 2016

$\endgroup$
-2
$\begingroup$

Can you calculate the indefinite integral of this function? I have tried several techniques, (I even tried using Wolfram Alpha) but no luck. I know that it converges but thats all I know. Here is the function though: f(x) = (-x^2)/((x^x)+x)

$\endgroup$
  • $\begingroup$ This would really be better suited as a comment; while it does make a small contribution to the post, it doesn't go towards answering the original question. $\endgroup$ – Robert Howard Mar 7 '18 at 18:38

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.