Path: news.mathworks.com!not-for-mail
From: <HIDDEN>
Newsgroups: comp.soft-sys.matlab
Subject: Re: couldn't find the reason of warning "Explicit integral could not be found"
Date: Sun, 11 Mar 2012 10:46:12 +0000 (UTC)
Organization: The MathWorks, Inc.
Lines: 49
Message-ID: <jjhvpk$plp$1@newscl01ah.mathworks.com>
References: <jjfo4l$1ri$1@newscl01ah.mathworks.com> <jjg8a9$idf$1@newscl01ah.mathworks.com>
Reply-To: <HIDDEN>
NNTP-Posting-Host: www-04-blr.mathworks.com
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
X-Trace: newscl01ah.mathworks.com 1331462772 26297 172.30.248.35 (11 Mar 2012 10:46:12 GMT)
X-Complaints-To: news@mathworks.com
NNTP-Posting-Date: Sun, 11 Mar 2012 10:46:12 +0000 (UTC)
X-Newsreader: MATLAB Central Newsreader 3372254
Xref: news.mathworks.com comp.soft-sys.matlab:760589

"Roger Stafford" wrote in message <jjg8a9$idf$1@newscl01ah.mathworks.com>...
> "Ozan" wrote in message <jjfo4l$1ri$1@newscl01ah.mathworks.com>...
> > I am having problem with my following code:
> > 
> > syms epsilon eta zeta;
> > ne=1;
> > me=1;
> > E1=70*10^9;
> > E2=200*10^9;
> > K1=76*10^9;
> > K2=150*10^9;
> > G1=26*10^9;
> > G2=78*10^9;
> > Vs=(((zeta/2)+(1/2))^ne)*((eta/2)^me);
> > f1=(G1.*(9.*K1+8.*G1))/(6.*(K1+2*G1));
> > Gasil=G1+(Vs.*(G2-G1))./(1+(1-Vs).*((G2-G1)./(G1+f1)));
> > Kasil=K1+(Vs.*(K2-K1))./(1+(1-Vs).*((3.*(K2-K1))./(3.*K1+4.*G1)));
> > Easil=(9.*Kasil.*Gasil)./(3.*Kasil+Gasil);
> > K11=(int(int(Easil,eta,-1,1),zeta,-1,1))
> > 
> > It does not give me any answer. Could someone help me?
> > 
> > Thanks 
> > 
> > Ozan
> - - - - - - - - -
>   Unless I am mistaken, the quantity 'Easil' can be expressed as the ratio of two quadratics in 'Vs'.  I see no reason why the symbolic toolbox cannot find an explicit solution for the indefinite double integral of such an expression.  Perhaps you are confusing 'int' with all the different constants you have defined, or perhaps writing 
> 
>  Vs=(((zeta/2)+(1/2))^ne)*((eta/2)^me);
> 
> instead of the simpler
> 
>  Vs = (zeta+1)*eta/4
> 
> is leading it astray.
> 
>   I would suggest not using 'ne' and 'me' since they are both equal to 1, and consolidating the other known constants into whatever coefficients occur in the above-mentioned quadratic ratio.  Then 'int' might succeed.  You will find the 'simple' and 'simplify' commands of great assistance in that endeavor.
> 
>   Another possibility is that with the given limits of integration for your definite integrals, the integrand becomes non-integrable - that is, it gives an infinite or indeterminate value.  Matlab might give up in such a case.  I would suggest you make a study of the above quadratic denominator to see where zeros might occur for zeta and eta values between -1 and +1.  If it is non-integrable, you are giving matlab an impossible task.
> 
> Roger Stafford

Thank you for your interest Roger,

Actually the values 'ne' and 'me' are not constant. I need to find the results for different 'ne' and 'me' values changing between zero and infinite. Because of this I can not simplify it.

Additionally, I changed the integral limits to see if the limits are cause of non-integrablity, but I saw that it is not related with the limits.

Regards