add interaction matrix method to register

[sgrava]

Resolves #417

add interaction_matrix method to Register

Description

From a given register, the interaction_matrix method should return a symmetric matrix encoding the Rydberg interactions $J_{ij}=1/r_{ij}^6$, with $r_{ij}=|r_{i}-r_{j}|$

Changes

• add Register.interaction_matrix method which return the Rydberg interaction matrix. Dispatches to torch or numpy depending on the coordinates type stored in the register
• test

Bonus

• adds matplotlib.use("Agg") in conftest.py. Totally unrelated but let the tests to avoid loading matplotlib in interacting mode. Saves 0.5 seconds per test module.

Next

• refactor abstract array interface explore refactoring array handling in a separate module #406

[github-actions]

PR Preview Action v1.8.1
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2026-08-04 06:27 UTC

[v-vitale]

Just a comment.

What is the reason behind using torch tensors for the interaction matrix?

[sgrava]

Just a comment.

What is the reason behind using torch tensors for the interaction matrix?

It would be nice to support torch backed registers as well, but not a priority for now I agree