[GRASS-user] r.damflood and Courant-Friedrich-Lewy stability condition

Roberto Marzocchi roberto.marzocchi at gmail.com
Thu Dec 31 03:02:23 PST 2015


I'm agree with Anna. In my opinion if the input are correct the warning is
only a warning and it is correct!
It is important in order to inform the user but the code is optimized in
order to automatically change the computational timestep (lower or higher)
in order to obtain the best performance without compromize the stability.

Perhaps you can do soem review n the html manual page in order to help
users to insert correct input?

All the best and happy new year ;-)

Eng. Roberto Marzocchi, PhD
R&D coordinator
Gter srl Innovazione in Geomatica, Gnss e Gis
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2015-12-31 1:16 GMT+01:00 Anna Petrášová <kratochanna a gmail.com>:

> Hi,
> On Wed, Dec 30, 2015 at 6:40 PM, Panagiotis Mavrogiorgos <pmav99 a gmail.com
> > wrote:
>> Hi all,
>> In r.damflood if you try to run a calculation using invalid input you get
>> a warning WRT Courant-Friedrich-Lewy stability condition
>> <https://en.wikipedia.org/wiki/Courant%E2%80%93Friedrichs%E2%80%93Lewy_condition>.
>> If the wikipedia article is accurate and it is indeed a necessary condition
>> for convergence wouldn't it make sense to raise a fatal error (or whatever
>> is more appropriate) as soon as the condition isn't respected? I mean I
>> don't see much point in running a potentially lengthy simulation that will
>> give meaningless results. Am I wrong in this?
> I was getting this warning several times in the beginning of the
> simulation, but the simulation still produced reasonable results. Lowering
> the time step would probably eliminate it. I think the warning is
> appropriate and shouldn't be changed to fatal error in my opinion, unless
> the original authors or anyone else who fully understands it say otherwise.
> Best,
> Anna
>> If my suggestion has indeed merit, could anyone suggest the most
>> appropriate way to do this?I don't mind submitting a patch but I am afraid
>> that I am not really familiar with GRASS C APIs.
>> These are the relevant lines:
>> https://trac.osgeo.org/grass/browser/grass-addons/grass7/raster/r.damflood/SWE.c#L504
>> https://trac.osgeo.org/grass/browser/grass-addons/grass7/raster/r.damflood/SWE.c#L708
>> thank you,
>> Panos
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