[MOAB-dev] Sparse vs. dense tags

[Paul Wilson]

So to make sure we have all the issues ...

* I don't think the inconsistency causes problems because the tags have 
the same interface regardless of what type they are.  (Other than 
performance) it doesn't matter how they are created because they will be 
used with the same interface either way.

* In this case we want to use sparse tags because we only need to tag 
surfaces.  There are very few surfaces and many entities, so sparse tags 
are better.

Paul

On 12/15/2010 04:23 PM, Tim Tautges wrote:
> It should be sparse.  The crucial difference is that when a dense tag 
> is given a value, all the entities in the same sequence as the one 
> whose tag is being set are also allocated storage for that tag.  In 
> the case of many sets, this would waste some storage.  It's a bigger 
> problem when tagging entities, though.
>
> - tim
>
> On 12/15/2010 03:09 PM, Steve Jackson wrote:
>> The "GEOM_SENSE_2" tag, used to record the volumes on either side of 
>> a surface, is not consistently created as either sparse or dense.  
>> When created from DagMC and its utility tools, the tag is created as 
>> dense, but when created from GeomTopoTool (via ReadCGM), the tag is 
>> sparse.
>>
>> Questions:
>>
>> * How big a problem is this inconsistency?  It doesn't seem to cause 
>> any errors or disruption.
>>
>> * Should the tag be dense or sparse?  The tag is only used on entity 
>> sets that represent surfaces, so my guess is that it ought to be 
>> sparse, but I don't understand the implementation difference deeply 
>> enough to be sure.
>>
>> ~S
>

-- 
-- ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ --
Paul Wilson ~ UW-Madison ~ 608-263-0807 ~ cal: http://bit.ly/pphw-cal
Associate Professor, Engineering Physics. ~ http://cnerg.engr.wisc.edu
Chair, Energy Analysis&  Policy Program ~ http://nelson.wisc.edu/eap
Note: I will be on sabbatical for the 2010-2011 academic year.


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