Bug Description

I am interested in using the windowed multipole (WMP) format to generate transient perturbed fission matrices, which requires the use of tally derivatives with respect to temperature. These tally derivatives are only supported when using WMP.

While exploring the implementation in multipole.py, I noticed that OpenMC relies on the external vectfit package, which is sourced from: https://github.com/liangjg/vectfit. However, that repository has not been maintained since 2020. This raises concerns about the long-term maintainability and compatibility of this dependency.

Steps to Reproduce

Not applicable – this is a support/development inquiry regarding external dependencies used in the WMP infrastructure.

Environment

• OS: Ubuntu 22.04
• OpenMC version: OpenMC 0.14.0
• Installation method: source build
• Nuclear data: JEFF33

Proposal / Request for Guidance

To improve long-term maintainability, I would like to contribute to OpenMC by integrating Jingang Liang's vectfit functionality natively into the OpenMC codebase (rather than relying on the unmaintained external repository).

• Is this integration of interest to the OpenMC development team?

• If yes, could you please guide me on the preferred approach to implement this within OpenMC?

  • Should this be done as a full reimplementation?
  • Is it preferable to preserve the existing API structure?

I would be happy to initiate a PR or work under the direction of a maintainer to ensure this contribution aligns with the overall architecture and roadmap of OpenMC.

Thank you for your guidance.