Torsten
Posts:
1,459
Registered:
11/8/10


Re: Warning: Explicit integral could not be found.
Posted:
Jul 22, 2013 9:38 AM


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 > closedform 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*(1exp(lams/2))
Best wishes Torsten.

