[Networkit] LAMG not converning for small tolerance

Henning Meyerhenke henning.meyerhenke at kit.edu
Mon Nov 7 09:23:11 CET 2016


Dear Simon,

Could you please pull and try the Dev branch? Michael Wegner, the LAMG
author, has pushed a quick fix. Does it solve your problem?

Best regards,
Henning


Am 06.11.16 um 16:19 schrieb Simon Adrian:
> Dear Moritz,
> 
> thank you for your reply.
> 
> The runtime for the entire program is less than 10 seconds, so I would rule 
> this out as the source of the problem.
> 
> Nevertheless, I have increased the value by a factor of ten, but as expected, 
> I could not observe any difference.
> 
> Best regards,
> Simon
> 
> 
> Am Freitag, 4. November 2016, 19:27:50 CET schrieb Moritz von Looz:
>> Dear Simon,
>>
>> thanks for your email and example!
>>
>> In both the original unit test and your example code, the maximum
>> convergence time is set to ten minutes with "status.maxConvergenceTime = 10
>> * 60 * 1000". It is to be expected that with increasing precision and input
>> size, the time until convergence grows until it no longer fits into the set
>> maximum.
>>
>> Do you mean it took unusually long and failed to converge even when
>> increasing the maximum time?
>>
>> All the best,
>> Moritz
>>
>> Am 02.11.2016 um 19:04 schrieb Simon Adrian:
>>> I have played around with the test example cpp/numerics/test/LAMGGTest.cpp
>>>  of the LAMG implementation.
>>>
>>> It works well when the I use the default tolerance (i.e.,
>>> status.desiredResidualReduction = 1e-6* b.length() /
>>> (hierarchy.at(0).getLaplacian() * x - b).length();)
>>>
>>> When I decrease the tolerance, it stops working at around 1e-10 for the
>>> "wing" graph, that is, it does not converge and the output for the final
>>> residual is "-nan".
>>>
>>> I'm not an expert in the LAMG algorithm, but it seems to me that this is
>>> not the correct behavior (given that there is some distance to machine
>>> precision from the tolerance).
>>>
>>> I compiled a slightly modified version without the googletest environment
>>> (see attachment); I presume that this should not effect the observation.
>>>
>>> Thank you very much for your help!
>>>
>>> Best regards,
>>> Simon
>>>
>>>
>>>
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>>
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> 
> 
> 
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-- 

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Karlsruhe Institute of Technology (KIT)
Institute of Theoretical Informatics (ITI)

Prof. Dr. Henning Meyerhenke
Theoret. Informatics / Parallel Computing

Phone: +49-721-608-41876
Web: http://parco.iti.kit.edu/henningm/

KIT - The Research University in the Helmholtz Association
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