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Potential 'output_writers' saving bug? #3614
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I've seen this before and yes I think it's a bug. Is there another issue open about this? I think there may be. @tomchor has a PR that is looking at this, we could use some extra eyes though. |
I also reported this on #3056, so maybe we should close this to avoid multiple issues of the same problem. I don't have a PR specifically trying to fix that, but it is possible that #3606 fixes, or least ameliorates, the issue. @mncrowe can you test your simulation on that branch and check if you see the same behavior? |
@mncrowe it sounds like this happened when you weren't using adaptive time-stepping --- which is nice because it will help us construct an MWE more easily. Do you think you can help with that? We just need a very simple simulation that reproduces the issue, hopefully something 0D with no dynamics that runs fast. |
@glwagner Will do. I'll remove the dynamics from my run and see if I can get a minimum not-working example. @tomchor I've downloaded that branch and will test when I can. Our system seems to have forgotten it's got GPUs post power cut so it's CPU only for now, I assume the underlying save functions are the same between devices? |
Yes. CPUs are even better for MWEs since we can run them from any laptop. Could you please post the MWE on #3056? That way we centralize the discussion there. |
I don't think the MWE even requires saving output. Can't we also achieve an MWE using a simple This issue should be independent of whether you are using the CPU or GPU. |
I've run a simulation with a timestep of$\Delta t = 1.066666...$ and it looks as though there's some kind of rounding bug which is resulting in multiple saves occasionally. I choose 'schedule = TimeInterval(t_end/num_saves)' and expect to get 'num_saves' (or possibly 'num_saves+1') points in the saved 'time' variable. However, I end up with about 30 extra saves. Examining 'time' in more detail reveals that most of the points are separated by 't_end/num_saves' but a few (around 30) are separated by a much smaller interval. My guess is that this is a rounding bug with when the code saves the field. Alternatively I could have messed something up.
Matt
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