[Stacked] Adds GLOBE Model updates for 3D + Dual Tree Traversal Acceleration

[peterdsharpe]

PhysicsNeMo Pull Request

Description

This PR includes:

• GLOBE model architecture modifications that fundamentally break the previous O(n^2) bottleneck, enabling scaling to large industrial problems. Scaling is now (both theoretically and empirically verified) to be O(n), which is very exciting to see for an all-to-all interaction problem. This is performed by doing a dual-tree variant of classical Barnes-Hut (or Fast-Multipole-Method-like) hierarchical acceleration by exploiting spatial locality. Normally Barnes-Hut would get you to O(n log n), but it turns out that by putting both the sources AND the targets in trees (a "dual tree traversal" approach), you can make it so that the interactions are no longer the bottleneck at all. This leaves O(n) operations as the bottleneck.
  • This dual-tree algorithm is implemented using a variant of a Linear Bounding Volume Hierarchy (LBVH), which is a nice way to make this more GPU-friendly (basically, this allows each layer of the tree (or in the case of dual tree traversal, each combination of layers from both trees) to coalesce into a single kernel launch, rather than doing a full tree traversal for every interaction.

Adds a theory doc about the dual tree traversal approach at ./physicsnemo/experimental/models/globe/hierarchical_acceleration.md.

This PR is:

• A split from the original now-split-up GLOBE 3D PR: Adds GLOBE 3D + Dual Tree Traversal Accelerations 🌎🌲  NVIDIA/physicsnemo#1481
• A stacked PR, to be merged only after Adds the PhysicsNeMo-Mesh changes required for GLOBE 3D NVIDIA/physicsnemo#1483 is merged.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.
• The CHANGELOG.md is up to date with these changes.
• An issue is linked to this pull request.
• If I am implementing a new model or modifying any existing model, I have followed the Models Implementation Coding Standards.

Dependencies

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