Drexel dragonThe Math ForumDonate to the Math Forum

Search All of the Math Forum:

Views expressed in these public forums are not endorsed by Drexel University or The Math Forum.

Math Forum » Discussions » Software » comp.soft-sys.matlab

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

Advanced Search

Back to Topic List Back to Topic List Jump to Tree View Jump to Tree View   Messages: [ Previous | Next ]

Posts: 1,627
Registered: 11/8/10
Re: Warning: Explicit integral could not be found.
Posted: Jul 22, 2013 9:38 AM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

Christopher Creutzig <Christopher.Creutzig@mathworks.com> wrote in message <51ECF984.7080907@mathworks.com>...
> 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

a is the second variable of integration - so it should not be part of the solution.
The solution for the integral
q = int(int(Q,b,0,sqrt((lams^2) - (a^2))),a,0,lams);
should come out as
q = 0.25*(1-exp(-lams/2))

Best wishes

Point your RSS reader here for a feed of the latest messages in this topic.

[Privacy Policy] [Terms of Use]

© Drexel University 1994-2015. All Rights Reserved.
The Math Forum is a research and educational enterprise of the Drexel University School of Education.