Friday, 16 August 2013

calculus - What are some examples where it is analytically easier to compute integrals than derivatives?




I know that in general, there exist more functions which are integrable than there are functions which are differentiable (nowhere differentiable to be exact), at least in C([0,1]), by the Baire Category Theorem. However, in general most elementary functions we know tend to have a derivative, which is generally almost always easier to compute than the integral. I have read in many places that functions or simulations where we need to compute either the derivative or integral analytically, the integral is easier. I can't find or think of any examples. Does anyone have any to shed light into this claim? Thanks!


Answer



I do not know, if this counts as an example, but let f denote any elementary, but "complicated" function, for example
f(x)=exp(sinx+23cosx+34)+xx+sinx
or whatever. Then define g(x):=f(logx)x. Then f is an elementary function, the antiderivative of g is flog (quite easy), and although it is possible to compute g analytically (first of course one has to compute f), I will not do this here.


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