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Topic: Warning: Explicit integral could not be found.
Replies: 4   Last Post: Jul 22, 2013 9:38 AM

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Christopher Creutzig

Posts: 231
Registered: 2/24/09
Re: Warning: Explicit integral could not be found.
Posted: Jul 22, 2013 5:21 AM
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On 26.06.13 03:26, Ferra wrote:

> I'm trying to solve this integration but it gives me this error:
> Warning: Explicit integral could not be found.
>
> syms a b
> Q = (1/(2*pi*lams)) * exp( - (a^2 + b^2)/(2*lams));
> q = int(int(Q,b,0,sqrt((lams^2) - (a^2))),a,0,lams);


I'm not sure what lams is, but even assuming it is an unspecified
symbolic variable, changing the order of integration yields a
closed-form integral:

>> syms lams
>> q = int(int(Q,a,0,lams),b,0,sqrt((lams^2) - (a^2)))


q =

(5734161139222659*pi*erf((2^(1/2)*lams)/2)*erf((2^(1/2)*(lams^2 -
a^2)^(1/2))/2))/72057594037927936


SMT neither has some explicit notion of ?double integral,? nor does it
check whether your integrand fulfills the conditions of Fubini's theorem
to allow exchanging the order of integration (which happens to be the
case here, at least if a, b, and lams are finite and real, and lams is
positive). That is something you need to do yourself.



HTH,

Christopher




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