[CIG-SHORT] "id" versus "label" for materials, faults, and boundary conditions

[Brad Aagaard]

Ravi-

Here is a more complete explanation of the differences between id and label 
values for materials, faults, and boundary conditions.

On Tuesday 05 February 2008, Ravi Kanda wrote:
> BTW, when I define a unique fault material id (different from 100, and
> other material IDs), do I have to create a corresponding material name in
> the material ODB file?  I guess I did not understand what you wanted me to
> try.

No, you do not need to include faults in the material ODB file. The materials 
ODB file sets the container for bulk materials. Faults are handled by the 
interfaces ODB file (interior interfaces container).

> So, here's the source of my confusion: It seems like it is necessary to
> associate the 'label' statements under each BC to the corresponding nodeset
> name/ID in the imported mesh.  I am assuming this is how pylith associates
> BC nodesets to BC names in the ODB file.  But this does not apply to
> materials, where all the pylith examples set 'label' to a text string
> ('elastic material'), and 'id' to the block name/ID in the imported mesh. 
> From what you say, fault definition follows the same rules as materials,
> and the label statements are just strings used for error-reporting; with
> 'id' statements linking nodesets to fault (or material) names in ODB files.
>  Perhaps the same rule applies to BCs too, but I just got "lucky"?

I realize label versus id for materials, bc, and faults is confusing. Much of 
this is due to the fact that mesh generators all do their own thing, and 
PyLith needed a common interface.

For materials, the "label" is a string used only for error messages. The id is 
an integer that corresponds to the material identifier in LaGriT (imt1) and 
CUBIT (block id). The id also tags the cells in the mesh for associating 
cells with a specific material and quadrature rule.

For BC, the "label" is a string used to associate groups of vertices (psets in 
LaGriT and nodesets in CUBIT) with vertices for a BC. I believe in 1.0.1 we 
had an "id", but we have since removed it because we were not using it.

For faults, the "label" is a string used to associated groups of vertices 
(psets in LaGriT and nodesets in CUBIT) with vertices on the fault. The "id" 
is a integer used to tag the cells in the mesh with a specific fault and 
quadrature rule. Because we use the "id" it to tag cohesive cells in the 
mesh, it must be unique among the faults as well as the materials.

Brad