Edge dW scan: unbracketed Newton in free_compute_wv_spline throws ConvergenceFailed

未关闭
  • 哪里不对？
#648 0 条评论 0 个 reaction 已指派 0 人 在 GitHub 查看

维护者通常 3 天内回复

还没有人认领这个 Issue。

评估

难度
3/5
预计耗时
1-2 天
新手友好度
74/100
Issue 类型
缺陷
描述清晰度
描述清楚
活跃度
活跃
技术栈
julia

调研方向

Read free_compute_wv_spline in src/ForceFreeStates/Free.jl and follow the call path through _handle_edge_dW_scan!, scan_edge_dW!, and findmax_dW_edge! in EulerLagrange.jl. Check how q_spline behaves over [dW_edge_scan_start, psilim], then reproduce the n = 1 edge scan if possible. Done means the scan completes when an unbracketed Newton solve would fail and existing converged cases retain the same roots.

由索引模型根据 Issue 内容生成。

描述

Summary

free_compute_wv_spline (src/ForceFreeStates/Free.jl) inverts q(ψ) at each edge-scan node using an unbracketed Roots.Newton() started from a ψ-linear guess. On one equilibrium in a parameter scan, Newton did not converge. The whole run then aborted with Roots.ConvergenceFailed("Algorithm failed to converge") during the n = 1 edge δW scan.

The same code is still on develop, at about line 222.

Where

qi   = qedge + (intr.qlim - qedge) * ((i - 1) / npsi)
psii = ctrl.dW_edge_scan_start + (intr.psilim - ctrl.dW_edge_scan_start) * ((i - 1) / npsi)
psi_array[i] = find_zero((psi -> profiles.q_spline(psi) - qi, psi -> profiles.q_deriv(psi)),
                         psii, Roots.Newton())

Call path: _handle_edge_dW_scan! → scan_edge_dW! → findmax_dW_edge! (EulerLagrange.jl:1140) → free_compute_wv_spline (Free.jl:232).

Context

  • Build: 728a7e7d5 (develop).
  • Settings: n = 1, no wall, psihigh = 0.998, mpsi = 256, grid_type = "core_edge_packed", dW_edge_scan_start = 0.97, and psilim set from rational_offset_fraction = 0.2.
  • The equilibrium is an H-mode with q95 ≈ 4, where q rises steeply over the last few percent in ψ. The g-file's FPOL is single precision, and GPEC already warns about that.
  • The failure came from one point of a 96-point scan. Its neighbors, with slightly lower and slightly higher pedestal-region current, ran normally, so the failure looks like Newton's sensitivity to its starting guess rather than a bad equilibrium.
  • I can't attach the equilibrium publicly, but I can share it privately.

Likely cause

The target q values are spaced evenly in q, while the starting guesses are spaced evenly in ψ. Where q(ψ) is strongly convex near the edge, the guess sits far from the root. A Newton step can then overshoot past psilim, into the spline's ExtendExtrap region, or oscillate.

Suggested fix

Over [dW_edge_scan_start, psilim], q is monotonic and the root is bracketed by construction. A bracketed solve would always converge:

psi_array[i] = find_zero(psi -> profiles.q_spline(psi) - qi,
                         (ctrl.dW_edge_scan_start, intr.psilim), Roots.Brent())

Alternatively, keep Newton and fall back to the bracketed solve when it fails. Wherever Newton converges today, either option returns the same root, so no existing result changes.

主要语言
Julia
星标
11
派生
7
平均合并
3 天 11 小时
30 天内合并 PR
68

环境准备

  • 没有 Dockerfile 或 Docker Compose 文件
  • 有 Pull Request 模板
  • 没有贡献指南

从这里开始

  1. 先读完整个 Issue，再读项目的贡献指南。
  2. 在 Issue 下留言说明你要接手 —— 这能避免两个人做同样的事。
  3. Fork 仓库，在一个分支上完成修改。
  4. 提交 Pull Request，并在描述里引用这个 Issue 编号。

OpenFUSIONToolkit/GPEC 的其他 Issue

查看 OpenFUSIONToolkit/GPEC 的全部 Issue

相似的 Issue

更多 Julia Issue

把新 issue 发到你的邮箱

精选适合新手参与的 GitHub issue 摘要。