Most people use either "init_each_timelevel", which calls the initial data routines several times (with different values in cctk_time), or "init_fill_timelevels", which initializes one time levels and copies these data to the past time levels. For TwoPunctions, only the latter makes sense. This leads to a zeroth order error on the past time levels, which translates to a first order error on the refinement boundaries, which translates to a second order error overall. I assume most people will just accept this error, since initial conditions are often inaccurate anyway ("junk radiation").
-erik
On Wed, Aug 4, 2021 at 2:21 PM Yosef Zlochower yosef@astro.rit.edu wrote:
Thanks Erik,
What algorithm do you suggest to initialize the past timelevels?
On 8/4/21 12:04 PM, Erik Schnetter wrote:
CAUTION: This message came from outside RIT. If you are unsure about the source or content of this message, please contact the RIT Service Center at 585-475-5000 or help.rit.edu before clicking links, opening attachments or responding.
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@astro.rit.edu wrote:
Hi,
I have been running into an issue where I when I interpolate anevolved 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@astro.rit.edu
CONFIDENTIALITY NOTE: The information transmitted, including attachments, is intended only for the person(s) or entity to which it is addressed and may contain confidential and/or privileged material. Any review, retransmission, dissemination or other use of, or taking of any action in reliance upon this information by persons or entities other than the intended recipient is prohibited. If you received this in error, please contact the sender and destroy any copies of this information.
Users mailing list Users@einsteintoolkit.org http://lists.einsteintoolkit.org/mailman/listinfo/users
-- 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@astro.rit.edu
CONFIDENTIALITY NOTE: The information transmitted, including attachments, is intended only for the person(s) or entity to which it is addressed and may contain confidential and/or privileged material. Any review, retransmission, dissemination or other use of, or taking of any action in reliance upon this information by persons or entities other than the intended recipient is prohibited. If you received this in error, please contact the sender and destroy any copies of this information.