Equilibrium - BUGFIX - Support original and rho grids for inverse equilibria

[StuartBenjamin]

Release note

• Audience: users
• Numerical impact: none for runs that worked before (solovev_n1 unchanged); grid_type = "original" and "rho" errored before for inverse equilibria (harness @ b182bbf)
• Migration: none

Inverse equilibria (CHEASE, LAR) now accept grid_type = "original" (the input file's own ψ nodes) and "rho" (uniform in √ψ).

Regression report

regress --cases solovev_n1 --refs bfc60610e,b182bbf68 (develop vs this head; julia 1.11.7, pinned manifest, 2 threads). No harness case uses an inverse equilibrium on these grids.

================================================================
Case: solovev_n1 — Solovev analytical equilibrium, n=1, ideal stability
================================================================

Regression Report: solovev_n1
=================================================================================
Ref 1: bfc60610e  @ bfc60610e (2026-10-09)
       env: julia 1.11.7, x86_64-linux-gnu, manifest fdfdedfa (pinned), 2 threads/2 BLAS, jit build
Ref 2: b182bbf68  @ b182bbf68 (2026-10-13)
       env: julia 1.11.7, x86_64-linux-gnu, manifest fdfdedfa (pinned), 2 threads/2 BLAS, jit build
---------------------------------------------------------------------------------
Quantity                      bfc60610e        b182bbf68        Diff       Status
---------------------------------------------------------------------------------
total energy Re(et[1])        3.429538e-01     3.429538e-01     0.0e+00    OK    
total energy Im(et[1])        -7.747105e-06    -7.747105e-06    0.0e+00    OK    
plasma energy Re(ep[1])       -1.005916e+01    -1.005916e+01    0.0e+00    OK    
vacuum energy Re(ev[1])       1.040211e+01     1.040211e+01     0.0e+00    OK    
vacuum matrix min eigenvalue  2.171292e+00     2.171292e+00     0.0e+00    OK    
plasma energy (all)           [32 elem]        [32 elem]        0.0e+00    OK    
vacuum energy (all)           [32 elem]        [32 elem]        0.0e+00    OK    
total energy (all)            [32 elem]        [32 elem]        0.0e+00    OK    
ODE steps (saved)             409              409              0.0e+00    OK    
ODE steps (total)             407              407              0.0e+00    OK    
q0                            1.900006e+00     1.900006e+00     0.0e+00    OK    
q95                           3.147422e+00     3.147422e+00     0.0e+00    OK    
beta_t                        4.621020e-02     4.621020e-02     0.0e+00    OK    
beta_n                        3.215791e+00     3.215791e+00     0.0e+00    OK    
# singular surfaces           2                2                0.0e+00    OK    
singular psi locations        [2 elem]         [2 elem]         0.0e+00    OK    
singular q values             [2 elem]         [2 elem]         0.0e+00    OK    
mpert                         32               32               0.0e+00    OK    
npert                         1                1                0.0e+00    OK    
q profile (checksum)          90ffc338a738...  90ffc338a738...  identical  OK    
pressure profile (checksum)   5040338aec07...  5040338aec07...  identical  OK    
ca_left (checksum)            6f1c35be5425...  6f1c35be5425...  identical  OK    
Runtime (s)                   208.6s           208.0s                      --    
=================================================================================
Summary: 22 unchanged

Notes for reviewers

• original set mpsi but never built the ψ grid, so the run stopped with an undefined-variable error. It now uses the input's own ψ nodes, without the axis node if the file has one (a ψ = 0 surface has no geometry). psilow and mpsi are ignored; psihigh still sets psilim, as in Fortran. No minimum node spacing is applied.
• rho was rejected as "Unsupported grid_type". It is uniform in √ψ from psilow to psihigh: ψᵢ = (√psilow + (√psihigh − √psilow)·i/mpsi)², i = 0…mpsi. Fortran's rho ignores psilow; here it honours psilow like the other grids.
• Test "Inverse grid types (original, rho)" in test/runtests_equil.jl, on the CHEASE test file INP1_binary: the original grid equals the file's nodes off the axis, the rho grid runs from psilow to psihigh, and every spline is finite for both. runtests_equil.jl: 299/299 pass.
• Replaces Equilibrium - BUGFIX - Support original and rho grids for inverse equilibria #521, without its axis-extrapolation code: psilow is always > 0, and the original grid now skips the axis node instead.
• Equilibrium - FEATURE - Read inverse i-files (ldp_i) such as TokaMaker save_ifile output #511 edits nearby lines in equilibrium_solver; whichever lands second may need a small rebase.

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🤖 Generated with Claude Code

[matt-pharr]

This looks fine, I will merge it