Equilibrium - Make the magnetic-axis search's singular-Jacobian threshold relative
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Assessment
- Difficulty
- 5/5
- Estimated time
- Over a week
- Newbie friendliness
- 38/100
- Issue type
- Feature
- Clarity
- Mostly clear
- Activity status
- Active
- Tech stack
- julia
Research direction
Start with Equilibrium/Axisymmetric/Direct.jl to inspect the Newton search and its singular_det check. Then check FastInterpolations' implementation or documentation for whether 2-D cubic_interp is C² or C¹. Done means the singular-Jacobian threshold scales with the equilibrium, and the fallback accounts for interpolation behavior that can make Newton cycle.
Written by the indexing model from the issue text.
Description
The Newton search for the magnetic axis (Equilibrium/Axisymmetric/Direct.jl) treats the Hessian of ψ as singular below singular_det = 1e-20, an absolute threshold in the units of ψ_RR·ψ_ZZ. Its meaning therefore depends on the device size and the field strength.
Proposal: compare the determinant with a scale built from the equilibrium, for example (ψ_axis − ψ_boundary)²/L⁴ with L the minor radius, so the same relative threshold applies to a compact device and to an ITER-sized one. Also confirm whether FastInterpolations' 2-D cubic_interp is C² or only C¹. If only C¹, the Hessian jumps at grid nodes and an axis near a node can make Newton cycle, which the fallback should then expect.
- Dominant language
- Julia
- Stars
- 11
- Forks
- 7
- Avg merge
- 4d 3h
- Merged PRs (30d)
- 70
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