[MOAB-dev] Dense tag behavior

[Tim Tautges]

On 05/13/2011 04:21 AM, Lorenzo Alessio Botti wrote:
>
> Hi all,
>
> It seems that dense tag memory is allocated when the tag is set for at
> least one entity of a given type.
>
> This is documented in the MOAB User's Guide. I missed it.
> "Storage for a given dense tag is not allocated until a tag value is set
> on an entity; memory for a given dense tag is allocated for all entities
> in a given sequence at the same time."
>
> I would have expected the dense tag to be associated with the default
> value to all the entities in the mesh.

It is; it's just that no *storage* is allocated for per-entity tag values until that tag value is set on one of the 
entities.  The default value is stored in a basic tag info datastructure for the tag, so it gets read from there.

- tim

>
> Thanks
> Lorenzo
>
>
>
> On May 12, 2011, at 4:43 PM, Tim Tautges wrote:
>
>> Probably when the tag was created, it was not created with a default
>> value. This could be the case if the vtk reader created it upon
>> finding it in the file.
>>
>> One way around this would be to create a tag of the proper name/data
>> type/storage type/default value before reading the vtk file; then the
>> vtk reader will use that tag, and your quads will get the default
>> value too.
>>
>> The tris being set has to do with how storage for tags is allocated
>> (based on sequences, the fundamental unit of storage in MOAB).
>>
>> - tim
>>
>> On 05/12/2011 09:31 AM, Lorenzo Botti wrote:
>>> I'm noticing a strange behavior of dense tags.
>>>
>>> I'm reading a hybrid tets+prisms+tris (tris represent the boundary
>>> mesh) vtk mesh where I have an id (type int) associated to each cell
>>> in order to define boundary conditions.
>>> The ids are correctly represented in MOAB as a dense tag over the
>>> mesh elements.
>>>
>>> However If I build 2D internal faces (tris and quads) with
>>> get_adjacencies only tris obtain the dense tag (set by default to 0?)
>>> while quads are tag free.
>>>
>>> Does it work this way because no tags have been associated to quads?
>>>
>>> Thanks
>>> Lorenzo
>>>
>>>
>>
>> --
>> ================================================================
>> "You will keep in perfect peace him whose mind is
>> steadfast, because he trusts in you." Isaiah 26:3
>>
>> Tim Tautges Argonne National Laboratory
>> (tautges at mcs.anl.gov <mailto:tautges at mcs.anl.gov>) (telecommuting from
>> UW-Madison)
>> phone: (608) 263-8485 1500 Engineering Dr.
>> fax: (608) 263-4499 Madison, WI 53706
>>
>

-- 
================================================================
"You will keep in perfect peace him whose mind is
   steadfast, because he trusts in you."               Isaiah 26:3

              Tim Tautges            Argonne National Laboratory
          (tautges at mcs.anl.gov)      (telecommuting from UW-Madison)
          phone: (608) 263-8485      1500 Engineering Dr.
            fax: (608) 263-4499      Madison, WI 53706