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Subject: Re: Warning: Explicit integral could not be found.
Date: Sun, 3 Jul 2011 01:24:09 +0000 (UTC)
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"Ashwin Balaji" <ashwinb1@umbc.edu> wrote in message <iuo7gj$oi7$1@newscl01ah.mathworks.com>...
> I need to Integrate the below function, but when I use the int(fun,R,1,2) command in Matlab it returns to me with an error saying "Explicit integral could not be found".
> 
> (2*R^-9) + (A*R^-11) / ((A+R^2)^2)
> 
> I am integrating over the limits [1,2] with respect to R and A is a constant. Could you please help and guide me through this problem. How do we obtain solutions to such Integrals using Matlab. I would come across many more similar integrals in my work which I would need to solve, so please guide me through the solution for these kind of problems.
> I need the answer for this integral to be in terms of constant A. So that further apply my conditions I could solve for A
> 
> Thanks,
> Ashwin
- - - - - - - - - -
  My own ancient version of 'solve' managed to handle that (with a rather messy solution.)  I don't see why later versions should be less skillful than mine.  Mine did make the rather unwarranted assumption that the quantity A+R^2 was always positive throughout the R range from 1 to 2 when it used log(A+R^2) in the indefinite integral at one point.  Perhaps your version is more careful about that and wants more information about A before committing itself.  If A is actually supposed to be positive, you might try using B^2 in place of A to see if that would remove its doubts since there is no chance that B^2+R^2 could be negative.

Roger Stafford