[Users] init_3_timelevels and nans on past timelevels

[Yosef Zlochower]

Thanks Erik,

  What algorithm do you suggest to initialize the past timelevels?


On 8/4/21 12:04 PM, Erik Schnetter wrote:
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>
> Yosef
>
> As you know, init_3_timelevels uses a special algorithm developed by
> Scott Hawley (see <https://arxiv.org/abs/gr-qc/0310042>) to initialise
> 3 time levels with initial conditions when you only have initial
> conditions for a single time. It uses a carefully orchestrated dance
> to step forward and backward in time, without having to do time
> interpolation (which isn't possible yet since there are no other time
> levels to interpolate from). The end result are (supposed to be) 3
> time levels full of good initial data that are second order accurate.
> To my knowledge, this algorithm is rarely used, and over time, it
> might be that a bug has crept in that would leave certain grid points
> uninitialized.
>
> As you do, I would have recommended using VisIt to analyze the
> resulting initial conditions and look for nans. I don't know how
> multiple time levels are mapped to VisIt variables; what you do looks
> correct. Another option would be to run the NaNChecker with its option
> to output all nan locations that it finds.
>
> -erik
>
>
> On Tue, Aug 3, 2021 at 9:41 PM Yosef Zlochower <yosef at astro.rit.edu> wrote:
>> Hi,
>>
>>     I have been running into an issue where I when I interpolate an
>> evolved function I get nans even though there are no nans on the
>> gridfunction itself. The nans appear to arise when the past timelevels
>> (at iteration 0) are initialized by init_3_timelevels and occur near the
>> buffer regions. As the evolution proceeds, these bad past timelevels are
>> overwritten with seemingly good data. Is this the expected behavior of
>> init_3_timelevels?
>>
>> Also, I have been trying to use visit to see what is going on. I used
>> CarpetIOHDF5::output_all_timelevels = true, and I think this means that
>> the past timelevels show up as different components of the same
>> gridfunction although I haven't been able to determine how the component
>> number is related to the actual components of the grid and the different
>> timelevels.
>>
>> Thanks
>>
>>
>> --
>> Dr. Yosef Zlochower
>> Center for Computational Relativity and Gravitation
>> Associate Professor
>> School of Mathematical Sciences
>> Rochester Institute of Technology
>> 85 Lomb Memorial Drive
>> Rochester, NY 14623
>>
>> Office:74-2067
>> Phone: +1 585-475-6103
>>
>> yosef at astro.rit.edu
>>
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-- 
Dr. Yosef Zlochower
Center for Computational Relativity and Gravitation
Associate Professor
School of Mathematical Sciences
Rochester Institute of Technology
85 Lomb Memorial Drive
Rochester, NY 14623

Office:74-2067
Phone: +1 585-475-6103

yosef at astro.rit.edu

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