[yt-dev] "faking" away variable-by-level refinement

Matthew Turk matthewturk at gmail.com
Thu May 23 12:13:46 PDT 2013


On Thu, May 23, 2013 at 3:10 PM, Chris Malone <chris.m.malone at gmail.com> wrote:
> Casey - Ok good, I didn't know there was anyone else who had used that
> feature.  One issue with a script to alter the dataset by adding levels is
> that I think BoxLib likes --- but perhaps doesn't _enforce_ --- there to be
> some padding between levels so that a coarse level isn't entirely covered by
> fine data.  Again, this could be remedied by interpolation, but I don't
> really care about the data on this intermediate level.  The approach within
> yt would be nice because it could simply ignore the data, possibly.
>
> Matt -
>>
>> > So, for the time being, I want to move forward with testing out the
>> > consolidated BoxLib frontend on a real dataset.  I could, of course,
>> > write a
>> > script offline that would take my old datafile, create
>> > intermediate-level
>> > grids and populate the data by averaging or interpolating the real data
>> > so
>> > that all levels have the same refinement ratio, but I've just "faked"
>> > the
>> > data for the levels that I have added.
>>
>> Ah, wow!  And have the tests worked so far?
>
>
> This was something that I could do, but have not yet.  I apologize if that
> was misleading!
>
>>
>> I have thought about this, and I believe it's quite reasonable.  For
>> what it's worth, we do something slightly similar with the RAMSES
>> frontend, in that we have a min_level that we assume it refines to.
>> (Not completely the same thing, but similar idea.)  There is a
>> mechanism for creating a fake grid, which is to set up a covering
>> grid, but that assumes the existence of a hierarchy already.  But it
>> might also be possible to fake the grid itself during the creation of
>> the hierarchy (setting a flag on it or something) and doubling up the
>> data.
>
>
> Ok, so there is some fake grid precedent.  I'll look at the Ramses code to
> get a feel for what is happening there.  If we don't actually care about the
> data on the fake grid, does it even need to be doubled?  It surely doesn't
> need to be a deep copy, but does data actually need to exist within the
> hierarchy at a specific level, or would that cause problems?

The RAMSES code in question unfortunately may not be completely
relevant, since it also assumes we have a base covering of the entire
domain at some min_level.  If we don't care about the data, I don't
think it will matter -- but if it does, we can address that, and it
should be an obvious failure.

>
> Chris
>
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