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Re: Solving difficult integral
*To*: mathgroup at smc.vnet.net
*Subject*: [mg18644] Re: Solving difficult integral
*From*: Paul Abbott <paul at physics.uwa.edu.au>
*Date*: Thu, 15 Jul 1999 01:45:39 -0400
*Organization*: University of Western Australia
*References*: <7mek2g$9il@smc.vnet.net>
*Sender*: owner-wri-mathgroup at wolfram.com
Christian Gudrian wrote:
> I need to solve the following integral:
>
> Integrate[Sqrt[C0+C1*x+C2*x^2+C3*x^3+C4*x^4],{x,0,t}]
Do you _really_ need to do this? If you re-write the integrand as
Integrate[Sqrt[(t - a) (t - b) (t - c) (t - d)], t]
Mathematica certainly will give you a rather complicated answer in terms
of elliptic functions -- but I question whether this answer will be all
that useful in practical situations.
It's analogous to asking if Mathematica can find a closed-form
expression for the roots of a cubic or quartic. It can -- but such
closed form expressions are rarely useful.
For any polynomial, Mathematica can represent the roots as Root objects
(and since Mathematica can do algebra with Root objects such a
representation is often more useful) so, effectively, the re-written
form is sufficient.
The real question is why do you need the general solution and, if you
have it, what do you want to do with it?
Cheers,
Paul
____________________________________________________________________
Paul Abbott Phone: +61-8-9380-2734
Department of Physics Fax: +61-8-9380-1014
The University of Western Australia
Nedlands WA 6907 mailto:paul at physics.uwa.edu.au
AUSTRALIA http://physics.uwa.edu.au/~paul
God IS a weakly left-handed dice player
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