Re: [h5md-user] Offset

[Konrad Hinsen]

Pierre de Buyl writes:

 > Some people work with [-L/2:L/2], others with [0:L].
 > 
 > offset is there so that users may dump their position data without
 > operation between memory and file, whatever box convention they use.

Do I conclude then that "offset" is supposed to be -L/2 in the first
case, and 0 in the second?


Olaf Lenz writes:

 > I was always wondering about the offset, but I didn't want to start that
 > discussion. Thanks, Konrad. :-/
 > 
 > The offset is mathematically irrelevant.

I agree.

 > I also do not see what the offset is needed for in the file.

I'd look at this from a different point of view: if it's there, what
information does it convey? What conclusion can a trajectory reader
draw from it?

 > The only case that I can think of where the offset might be useful is,
 > when it is somehow guaranteed that the positions are all within the
 > primary image that is defined by the offset and the edges.

Exactly.

 > Therefore, from my point of view, the offset is useless and can be
 > removed from the specs.

Or add a guarantee about the positions being in the primary image to
the specs. From my experience, that can be useful information to have.

Konrad.
-- 
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Konrad Hinsen
Centre de Biophysique Moléculaire, CNRS Orléans
Synchrotron Soleil - Division Expériences
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91192 Gif sur Yvette Cedex, France
Tel. +33-1 69 35 97 15
E-Mail: research AT khinsen DOT fastmail DOT net
http://dirac.cnrs-orleans.fr/~hinsen/
ORCID: http://orcid.org/0000-0003-0330-9428
Twitter: @khinsen
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