Discovering the capabilities of t8code for my needs

[CsatiZoltan]

Feel free to move this issue to the Discussions; I opened an issue as I cannot open a discussion thread.

I collected a lot of materials (theses, presentation, etc.) about t8code, and I think it would suit my needs. However, before settling with this code, I would like to make sure that it is indeed the right tool.

Goal

A high-order solution exists on a high-order mesh. We want to replace the high-order solution and the high-order cells with an approximate solution on linear cells. Hence, we want to use AMR for post-processing, not for solving.

Characteristics of the problem

• Large unstructured mesh up to a few billion elements
• Mesh is distributed on several processors
• Full quad (2D) or full hexa (3D)
• Non-isoparametric elements: high-order element geometry with a high-order solution (e.g. DGSEM)

Requirements

• Can handle large number of trees (one tree for one original high-order element, I guess)
• Non-duplicate nodes on a subdomain, i.e. a "standard" finite element mesh with a single field value associated with a given node.
• At the end of the AMR procedure, be able to create the explicit mesh (essential for post-processing) based on the initial coarse mesh and the space filling curve
• Geometrical information available to the callback function: for a given forest leaf, I need to know where it is located in the real space so that I can perform the interpolation of the high-order solution. That will serve as an indicator whether to refine the element or not.

Nice to have

• Hybrid meshes that may arise in the future
• Elimination of hanging nodes
• Hanging node elimination not by cutting all the quad/hexa cells to tri/tetra cells, but by keeping as many quad/hexa cells as possible and only including a few transition cells
• Global connectivity across subdomains (i.e. all trees are merged so there will be no duplicate nodes even on subdomain boundaries)
• Data structure that can use existing memory to avoid data copy whenever possible.

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Based on the demands, is t8code an appropriate tool for me? If not, could you please point me to alternatives?

Thanks,
Zoltan

[jmark]

Hello @CsatiZoltan !

Welcome to t8code!

At a first glance, your given goals, problem description and requirements are a nice match with the capabilities t8code offers. For the nice-to-have section, I can say we already support hybrid meshes. Resolving hanging nodes exactly in the manner as you described is work-in-progress but will be part of t8code in the midterm future. About global connectivity across subdomains and in-place datastructures is, to my knowledge, not available as of now but, of course, nice to have.

[jmark]

Let us know if we can be of help in your project! Do not hesitate to ask if you have more questions!

[CsatiZoltan]

Hi @jmark,

Thank you for the rapid and reassuring reply.

I would certainly have questions, but those are more specific to certain steps of the AMR process. I thought about restricting this issue to the features of t8code, while opening new ones concerning the concrete workflow. Moreover, since these will not be developer's issues, you could give me right to open discussion threads. What do you think?