hodogram

A plot of one vector component against another over time, forming a curve that shows how the vector changes. For magnetic fields, its shape can indicate linear, circular, or elliptical polarization and its direction shows the rotation sense.

In plain words
What is it for?
Use it to inspect magnetic fluctuations, classify their polarization, determine rotation direction, or study field changes across boundaries such as the magnetopause or current sheet.
Why use it?
It makes wave polarization and magnetic-field rotation easier to recognize than separate component-versus-time plots.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/spedas/spedas_agent_kit/hodogram
Any agent
npx skills add spedas/spedas_agent_kit --skill hodogram
Clone the repo
git clone --depth 1 https://github.com/spedas/spedas_agent_kit

Made for: Claude Code, Codex.

Per session 85 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,478 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00085 $0.01478
Opus 5 $0.00043 $0.00739
Sonnet 5 $0.00017 $0.00296
Haiku 4.5 $0.00009 $0.00148

Measured 3d ago against content hash e9ee92ba9e8e, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

hodogram scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 3d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.agents/plugins/spedas-codex/skills/hodogram/SKILL.md · 67 lines

How it starts

The opening of the file, as written. The whole thing — 67 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Hodogram: component-vs-component polarization plot

A hodogram plots one vector component against another (e.g. B in the maximum- vs intermediate-variance direction) as a parametric curve traced over time. Its shape reveals polarization — a line (linear), a circle (circular), an ellipse (elliptical) — and the direction the curve is traced gives the rotation sense. It is the standard companion to minimum-variance analysis (MVA) for classifying waves and characterizing boundary rotations (e.g. magnetopause/current-sheet field rotation). This skill composes existing tools — render_tplot gained scatter/x-y panels (#120/#123), so no new tool is added.

When to use

  • "Plot the hodogram of B for this interval" / "is this fluctuation linear, circular, or elliptical?"
  • "Which way does B rotate across this boundary?" (rotation sense / handedness).
  • The polarization companion to boundary-minimum-variance — view B_max vs B_int in the LMN frame.

Tool chain (all already exist)

create_spedas_analysis_bundlefetch_data_product (B vector) → (analyze_minvar_coordinates to get the LMN/variance frame, recommended) → transform_timeseries_coordinates or the MVA-rotated series → write one .npz matrix of the two components → render_tplot(panel_types=["scatter"], x_component, y_component).

Backend (VERIFIED contract)

The hodogram is produced by render_tplot's scatter/x-y panel (added in #123):

  • render_tplot(input_files=[npz], output_file=..., panel_types=["scatter"], x_component=[i], y_component=[j], ...) renders one 2-D matrix per .npz as a parametric x-y plot of column i vs column j (defaults 0 vs 1). panel_types may also use "xy"; it overrides the per-file default. x_component/y_component are lists of column indices, one per input file. Mismatched lengths return a structured invalid_argument error (validated before any drawing).
  • One matrix per file: to plot B_max-vs-B_int and B_max-vs-B_min as two panels, write two .npz inputs (or pass the same file twice with different x_component/y_component), not one multi-key file expecting a multi-panel stack.
  • Input .npz holds the vector as an N×k data matrix (component columns) and a time axis; the scatter panel ignores time for positioning but uses the row order to trace the curve.
  • Verified live: a 2-column circular series rendered with panel_types=["scatter"], x_component=[0], y_component=[1] returns status: success and writes a PNG.

Read the full file on GitHub · 67 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 3d ago First seen · 67 lines · 85 tokens per session scan A e9ee92ba9e8e

Subscribe to this mod's changes

hodogram is a skill published in the GitHub repository spedas/spedas_agent_kit (3 stars, last pushed 1mo ago), licensed MIT. It adds 85 tokens to every session and 1,478 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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