integrate function
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Hey,
i want to integrate the function di on an interval from 1 to infinity. di=(sinh((b.*x)./a)./sinh((pi.*x)./a));
However while using quadgk matlab returns the following error code: Warning: Infinite or Not-a-Number value encountered.
Is there a possibility to change to change the code so maybe that it lowers accuracy however a result is obtained? Or is there another function that evaluates integrals up to infinity?
Thanks in advance.
采纳的回答
Mike Hosea
2012-6-6
The problem has nothing to do with the integrator, rather with the way you have written the integrand:
>> a = 1; b = 1;
>> di= @(x)(sinh((b.*x)./a)./sinh((pi.*x)./a));
>> di(1000)
ans =
NaN
You're giving the integrator NaN values, so there's not much it, or any other code, can do with that. Try multiplying your integrand numerator and denominator by exp(-pi*x) and simplifying. I get
>> dj= @(x)(exp((b-pi)*x) - exp(-(b+pi)*x))./(1-exp(-2*pi*x))
dj =
@(x)(exp((b-pi)*x)-exp(-(b+pi)*x))./(1-exp(-2*pi*x))
>> dj(1000)
ans =
0
>> quadgk(dj,1,inf)
ans =
0.051035297097439
-- Mike
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