NetSpectra

Higher‑order statistics for hybrid (farm + region) dynamic movement networks.
A compact simulator and analysis scaffold for temporal edge/node appearance, random‑walk mass, and directed spectral signatures (magnetic Laplacian).

---

What is NetSpectra?

NetSpectra proposes a hybrid dynamic graph representation for livestock movement networks:

• Keep farm-level detail inside one focal region (e.g., a COROP region in NL),
• Contract everything outside into regional supernodes and superflows,
• Analyze day-by-day dynamics with higher‑order statistics that go beyond static degree counts.

This lets you preserve local detail where you care most, while still retaining a coherent national “context backbone”.

For formal definitions and interpretation guides, see My Blog Post

Network simulator	Higher-order statistics

---

What’s included

• An interactive D3 simulator that generates a 10‑day hybrid network on the NL COROP map and visualizes:
  • TEA / TNA: temporal edge / node appearance (new / reactivated / persistent / churn)
  • π‑mass: stationary random-walk mass on Farms vs Regions (LIC-restricted)
  • Magnetic Laplacian spectra: directed spectral signatures (with quality + weighting toggles)
• COROP boundaries + label points (nl_corop.geojson, nl_corop_labelpoint.geojson)

If you fork this for a different country, replace the two GeoJSONs in assets/files/ and preserve the statcode / statnaam fields, or update the property lookups in the HTML.

---

Quickstart

1) Clone

git clone https://github.com/EvoLandEco/netspectra.git
cd netspectra

2) Serve the repository root

Browsers block fetch() from file://, so run a tiny local server from the repo root:

python -m http.server 8000

3) Open in browser

http://localhost:8000/hybrid_simulator.html

Keep the bundled asset paths in place (or update the paths inside the HTML):

• assets/files/nl_corop.geojson
• assets/files/nl_corop_labelpoint.geojson

The simulator currently loads D3, Turf, numeric.js, and iframe-resizer from public CDNs, so the browser session needs internet access unless you vendor those dependencies locally.

---

How the simulator works

Each run builds a 10-day directed hybrid network. The selected focal COROP is represented at farm level: nFarms farm nodes are sampled inside the focal polygon, while every non-focal COROP becomes one regional supernode positioned at its label point.

Eligible directed pairs are split into four blocks: farm→farm, farm→region, region→farm, and region→region. On each day, yesterday’s edges persist with probability p_keep; all remaining eligible pairs can appear as new edges with probability pBirthFF for farm→farm pairs and pBirthX for every cross-region block. Each new edge receives a simulated positive trade volume, and persisted edges keep their volume with a small random perturbation.

Statistics are computed from each day’s directed graph as follows:

• TEA / TNA compare the current edge set or active-node set with the previous day and report persistent, reactivated, new, and churned activity, plus average novelty and persistence ratios across the 10 days.
• π-mass builds a lazy row-stochastic walk, restricts it to the day’s largest irreducible / strongly connected component, computes the stationary distribution, and sums that mass over farm nodes versus region nodes.
• Magnetic spectra build a normalized magnetic Laplacian from the directed adjacency matrix. Fast computes every other day and linearly interpolates skipped days, Balanced computes daily on the active induced subgraph, and Full computes daily on the full hybrid node set.
• Weight mode affects π-mass and magnetic spectra only: Unweighted treats every edge as weight 1, while Weighted uses the simulated trade volumes.

---

How to use

1. Pick a focal region and farm count (5-100).
2. Tune network dynamics:
   • p_keep controls persistence of yesterday’s edges,
   • Birth prob inside FF controls new farm→farm edges,
   • Birth prob (FR/RF/RR) controls new farm↔region and region→region edges.
3. Use the Day slider to step through time.
4. Use the Unweighted / Weighted switch to decide whether:
   • π‑mass and magnetic spectra treat each edge equally (unweighted), or
   • they incorporate simulated trade volume (weighted).
5. Use Spectrum quality to trade speed for fidelity:
   • Fast samples spectra every other day and interpolates the skipped days,
   • Balanced computes spectra daily on the active induced subgraph,
   • Full computes spectra daily on the full hybrid node set.

The status badge in the map panel shows progress; hover it to reveal Cancel while heavy computations run.

---

Embedding in a blog

The simulator supports:

• automatic height resizing using iframe-resizer, and
• dark-mode sync with a site-level #darkmode checkbox (if present).

See the embedding snippet and explanation in:
https://qtj.me/blog-hybrid-corop-farm.html

---

Acknowledgements

NetSpectra’s simulator uses:

• D3.js for visualization,
• Turf.js for point-in-polygon sampling,
• numeric.js for eigen-decomposition in the Web Worker,
• iframe-resizer for clean iframe embedding.

---

License

MIT License.