what is the material id after coarsening

[Zhibo Luo]

Hi guys,

I encountered a problem recently when I refine and coarse mesh. I know the material id is inherited from mother to child cell upon mesh refinement. But what is the rules when coarsening the mesh? For example, in 2D, I have four neighbored cells which have different material ids, then what is the material id when these four cells are combined into one cell? what I should do if I want to coarsening the cells with the same material id?

[Wolfgang Bangerth]

It's just the same value as you set before you refined the cell originally.

When you refine cells, the children are new and we need a rule what
their material_ids should be. But when you coarsen these children again,
then the mother cell you get has been there all along -- so we need no
rule what material_id it should get, it just retains the material_id it
has always had.

Best
W.

--
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Wolfgang Bangerth email: bang...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/

[Zhibo Luo]

Thank you Prof. Wolfgan. I just realize that. So if I want to coarsen the neighbored cells with the same material id, I should find their parent cell and set the same material id. Is this right?

Best regards,

Zhibo

在 2017年9月13日星期三 UTC-4上午11:49:38，Wolfgang Bangerth写道：

[Wolfgang Bangerth]

On 09/13/2017 09:59 AM, Zhibo Luo wrote:
> Thank you Prof. Wolfgan. I just realize that. So if I want to coarsen
> the neighbored cells with the same material id, I should find their
> parent cell and set the same material id. Is this right?

You can.

What I'm saying is that if you had set the material_id of a cell (say,
to a value of 42) before it was refined and replaced by its children,
then after coarsening these children the parent cell will still have the
value 42.