integration accuracy

integration accuracy - Wrong numerical answer for simple integration of 1/ln(x) - Messages

#1 Posted: 5/22/2017 6:28:13 PM
Joey Ooi

Joey Ooi

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The integral of 1/(ln(x) with limits of x from 2 to 1000 does not agree with mathlab or maxima --
The numerical value of the following integration is off -- should be 176.56 and Smath gives 177.1
Any idea what could be the problem?
Thanks
Joey Ooi

#2 Posted: 5/22/2017 6:50:40 PM
Davide Carpi

Davide Carpi

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Hello [userlink]Joey Ooi[/userlink],

You have to set a better accuracy in the global options (tools >> options >> calculation)

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#3 Posted: 5/22/2017 9:32:54 PM
Joey Ooi

Joey Ooi

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Thank you for your quick and accurate response Davide.
It was very helpful indeed.
Best regards
Joey
#4 Posted: 5/23/2017 7:53:55 AM
Jean Giraud

Jean Giraud

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Wrote

Any idea what could be the problem?



Smath Simpson iterative integrator is known to range from
exact [sometimes] to poor. Increasing accuracy is fine in
this example but will not converge in other instances like
in the Fourier Quantum double integral. You can rescue
your example using the attached Romberg.
Mathematica online integrator link added.

Jean

Integrate Mathematica.sm (9 KiB) downloaded 63 time(s).



#5 Posted: 5/23/2017 8:37:48 AM
Jean Giraud

Jean Giraud

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... revisit same work sheet for the 7 decimals !

Jean

Integrate Mathematica.sm (10 KiB) downloaded 60 time(s).
#6 Posted: 5/23/2017 8:53:58 AM
Jean Giraud

Jean Giraud

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... like this

Romberg Integrator.gif
#7 Posted: 5/23/2017 2:32:33 PM
Jean Giraud

Jean Giraud

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How many numerical integrators have been imagined ?
1+1+1+... Even Mathcad aren't so easy to deal with.
This visit is worth the time spent.

Jean

Fourier Quantum CoC Model.sm (36 KiB) downloaded 56 time(s).
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