# Algorithm Refinement & ML Training Implementation Plan

> **For Claude:** REQUIRED SUB-SKILL: Use superpowers:executing-plans to implement this plan task-by-task.

**Goal:** Refine the propagation scoring algorithm using 58K QSOs matched to HRRR conditions, update algo.md and scorer code, then train the Axon ML model for fast HRRR-based prediction.

**Architecture:** Analysis mix task extracts QSO↔HRRR correlations → findings drive scorer/algo.md updates → recomputed scores become ML training data → trained model integrates into grid worker with algorithm fallback.

**Tech Stack:** Elixir/Ecto (analysis queries), Nx/Axon/EXLA (ML training), PostgreSQL (data source)

---

### Task 1: Analysis Mix Task — QSO-HRRR Dataset Builder

**Files:**
- Create: `lib/mix/tasks/propagation_analyze.ex`
- Test: `test/mix/tasks/propagation_analyze_test.exs`

**Step 1: Write the failing test**

```elixir
# test/mix/tasks/propagation_analyze_test.exs
defmodule Mix.Tasks.PropagationAnalyzeTest do
  use Microwaveprop.DataCase

  alias Mix.Tasks.PropagationAnalyze

  describe "build_dataset/0" do
    test "returns list of QSO-condition maps with required keys" do
      # Insert a QSO with known position and timestamp
      qso = insert_qso(
        band: 10_000,
        distance_km: 200.0,
        qso_timestamp: ~N[2023-06-15 12:00:00],
        pos1: %{"lat" => 33.0, "lng" => -97.0},
        pos2: %{"lat" => 34.0, "lng" => -96.0}
      )

      # Insert HRRR profiles at the grid points nearest to both endpoints
      insert_hrrr_profile(
        lat: 33.0, lon: -97.0, valid_time: ~N[2023-06-15 12:00:00],
        surface_temp_c: 30.0, surface_dewpoint_c: 20.0,
        surface_pressure_mb: 1010.0, min_refractivity_gradient: -100.0,
        hpbl_m: 500.0, pwat_mm: 30.0, surface_refractivity: 330.0,
        ducting_detected: false
      )

      insert_hrrr_profile(
        lat: 34.0, lon: -96.0, valid_time: ~N[2023-06-15 12:00:00],
        surface_temp_c: 28.0, surface_dewpoint_c: 18.0,
        surface_pressure_mb: 1012.0, min_refractivity_gradient: -80.0,
        hpbl_m: 600.0, pwat_mm: 25.0, surface_refractivity: 320.0,
        ducting_detected: false
      )

      [row] = PropagationAnalyze.build_dataset()

      assert row.qso_id == qso.id
      assert row.band == 10_000
      assert row.distance_km == 200.0
      assert row.month == 6
      assert row.utc_hour == 12
      assert_in_delta row.avg_surface_temp_c, 29.0, 0.01
      assert_in_delta row.avg_min_refractivity_gradient, -90.0, 0.01
      assert_in_delta row.avg_hpbl_m, 550.0, 0.01
    end

    test "skips QSOs without HRRR match at either endpoint" do
      insert_qso(
        band: 10_000, distance_km: 200.0,
        qso_timestamp: ~N[2023-06-15 12:00:00],
        pos1: %{"lat" => 33.0, "lng" => -97.0},
        pos2: %{"lat" => 34.0, "lng" => -96.0}
      )

      # Only insert one endpoint's HRRR profile
      insert_hrrr_profile(
        lat: 33.0, lon: -97.0, valid_time: ~N[2023-06-15 12:00:00],
        surface_temp_c: 30.0, surface_dewpoint_c: 20.0,
        surface_pressure_mb: 1010.0, min_refractivity_gradient: -100.0,
        hpbl_m: 500.0, pwat_mm: 30.0
      )

      assert PropagationAnalyze.build_dataset() == []
    end
  end
end
```

**Step 2: Run test to verify it fails**

Run: `mix test test/mix/tasks/propagation_analyze_test.exs --trace`
Expected: FAIL — module not defined

**Step 3: Write test helpers**

Add to `test/support/fixtures.ex` (or create if missing) — helper functions `insert_qso/1` and `insert_hrrr_profile/1` that insert records directly via Repo.

**Step 4: Write minimal implementation**

```elixir
# lib/mix/tasks/propagation_analyze.ex
defmodule Mix.Tasks.PropagationAnalyze do
  @shortdoc "Analyze QSO-HRRR correlations for algorithm refinement"
  @moduledoc """
  Builds a dataset matching QSOs to HRRR atmospheric conditions at both
  endpoints, then runs correlation analysis against QSO distance.

  ## Usage

      mix propagation.analyze
  """

  use Mix.Task

  import Ecto.Query

  alias Microwaveprop.Repo

  @impl Mix.Task
  def run(_args) do
    Application.put_env(:microwaveprop, Oban, queues: false)
    Mix.Task.run("app.start")

    IO.puts("Building QSO-HRRR analysis dataset...")
    dataset = build_dataset()
    IO.puts("Matched #{length(dataset)} QSOs to HRRR conditions")

    IO.puts("\n=== CORRELATION ANALYSIS ===\n")
    run_correlation_analysis(dataset)

    IO.puts("\n=== FACTOR ANALYSIS ===\n")
    run_factor_analysis(dataset)

    IO.puts("\n=== INTERACTION EFFECTS ===\n")
    run_interaction_analysis(dataset)

    IO.puts("\nDone. Use findings to update algo.md and scorer.ex")
  end

  @doc """
  Builds the QSO-HRRR matched dataset.

  For each QSO with valid positions and a timestamp within HRRR range (2016+),
  finds the nearest HRRR grid point to each endpoint (rounded to 0.125°) at
  the nearest hour. Averages atmospheric conditions across both endpoints.

  Returns a list of maps with:
  - qso_id, band, distance_km, month, utc_hour
  - avg_surface_temp_c, avg_surface_dewpoint_c, avg_surface_pressure_mb
  - avg_min_refractivity_gradient, avg_hpbl_m, avg_pwat_mm
  - avg_surface_refractivity, ducting_either (boolean)
  - terrain_verdict
  """
  def build_dataset do
    # Query uses a CTE to round QSO positions to HRRR grid and truncate timestamps,
    # then joins to hrrr_profiles at both endpoints, averaging atmospheric values.
    query = """
    WITH qso_grid AS (
      SELECT
        q.id AS qso_id,
        q.band::integer AS band,
        q.distance_km,
        EXTRACT(MONTH FROM q.qso_timestamp)::integer AS month,
        EXTRACT(HOUR FROM q.qso_timestamp)::integer AS utc_hour,
        ROUND(CAST((q.pos1->>'lat')::float * 8 AS numeric)) / 8 AS grid_lat1,
        ROUND(CAST((q.pos1->>'lng')::float * 8 AS numeric)) / 8 AS grid_lng1,
        ROUND(CAST((q.pos2->>'lat')::float * 8 AS numeric)) / 8 AS grid_lat2,
        ROUND(CAST((q.pos2->>'lng')::float * 8 AS numeric)) / 8 AS grid_lng2,
        date_trunc('hour', q.qso_timestamp) AS match_time
      FROM qsos q
      WHERE q.distance_km < 3000
        AND q.distance_km > 0
        AND q.qso_timestamp >= '2016-06-30'
        AND q.pos1->>'lng' IS NOT NULL
        AND q.pos2->>'lng' IS NOT NULL
    )
    SELECT
      qg.qso_id, qg.band, qg.distance_km, qg.month, qg.utc_hour,
      (COALESCE(h1.surface_temp_c, h2.surface_temp_c) +
       COALESCE(h2.surface_temp_c, h1.surface_temp_c)) / 2.0 AS avg_surface_temp_c,
      (COALESCE(h1.surface_dewpoint_c, h2.surface_dewpoint_c) +
       COALESCE(h2.surface_dewpoint_c, h1.surface_dewpoint_c)) / 2.0 AS avg_surface_dewpoint_c,
      (COALESCE(h1.surface_pressure_mb, h2.surface_pressure_mb) +
       COALESCE(h2.surface_pressure_mb, h1.surface_pressure_mb)) / 2.0 AS avg_surface_pressure_mb,
      (COALESCE(h1.min_refractivity_gradient, h2.min_refractivity_gradient) +
       COALESCE(h2.min_refractivity_gradient, h1.min_refractivity_gradient)) / 2.0 AS avg_min_refractivity_gradient,
      (COALESCE(h1.hpbl_m, h2.hpbl_m) +
       COALESCE(h2.hpbl_m, h1.hpbl_m)) / 2.0 AS avg_hpbl_m,
      (COALESCE(h1.pwat_mm, h2.pwat_mm) +
       COALESCE(h2.pwat_mm, h1.pwat_mm)) / 2.0 AS avg_pwat_mm,
      (COALESCE(h1.surface_refractivity, h2.surface_refractivity) +
       COALESCE(h2.surface_refractivity, h1.surface_refractivity)) / 2.0 AS avg_surface_refractivity,
      COALESCE(h1.ducting_detected, false) OR COALESCE(h2.ducting_detected, false) AS ducting_either,
      tp.verdict AS terrain_verdict
    FROM qso_grid qg
    JOIN hrrr_profiles h1
      ON h1.lat = qg.grid_lat1 AND h1.lon = qg.grid_lng1 AND h1.valid_time = qg.match_time
    JOIN hrrr_profiles h2
      ON h2.lat = qg.grid_lat2 AND h2.lon = qg.grid_lng2 AND h2.valid_time = qg.match_time
    LEFT JOIN terrain_profiles tp ON tp.qso_id = qg.qso_id
    ORDER BY qg.band, qg.distance_km DESC
    """

    Repo.query!(query, [], timeout: 300_000).rows
    |> Enum.map(fn row ->
      [qso_id, band, distance_km, month, utc_hour,
       avg_temp, avg_dewpoint, avg_pressure, avg_gradient,
       avg_hpbl, avg_pwat, avg_refractivity, ducting_either,
       terrain_verdict] = row

      %{
        qso_id: qso_id,
        band: band,
        distance_km: distance_km,
        month: month,
        utc_hour: utc_hour,
        avg_surface_temp_c: avg_temp,
        avg_surface_dewpoint_c: avg_dewpoint,
        avg_surface_pressure_mb: avg_pressure,
        avg_min_refractivity_gradient: avg_gradient,
        avg_hpbl_m: avg_hpbl,
        avg_pwat_mm: avg_pwat,
        avg_surface_refractivity: avg_refractivity,
        ducting_either: ducting_either,
        terrain_verdict: terrain_verdict
      }
    end)
  end

  # --- Correlation analysis ---

  defp run_correlation_analysis(dataset) do
    bands = [10_000, 24_000, 47_000, 75_000]

    for band <- bands do
      band_data = Enum.filter(dataset, &(&1.band == band))
      next_if_empty(band_data, band, fn ->
        IO.puts("--- Band: #{div(band, 1000)} GHz (n=#{length(band_data)}) ---")
        distances = Enum.map(band_data, & &1.distance_km)

        variables = [
          {:avg_surface_temp_c, "Surface Temp (C)"},
          {:avg_surface_dewpoint_c, "Dewpoint (C)"},
          {:avg_surface_pressure_mb, "Pressure (mb)"},
          {:avg_min_refractivity_gradient, "Refr. Gradient (N/km)"},
          {:avg_hpbl_m, "BL Depth (m)"},
          {:avg_pwat_mm, "PWAT (mm)"},
          {:avg_surface_refractivity, "Surface Refractivity"},
          {:month, "Month"},
          {:utc_hour, "UTC Hour"}
        ]

        for {key, label} <- variables do
          values = Enum.map(band_data, &Map.get(&1, key))
          corr = spearman_correlation(values, distances)
          bar = correlation_bar(corr)
          IO.puts("  #{String.pad_trailing(label, 25)} r=#{format_corr(corr)} #{bar}")
        end

        IO.puts("")
      end)
    end
  end

  # --- Factor analysis (binned median distance) ---

  defp run_factor_analysis(dataset) do
    band_10g = Enum.filter(dataset, &(&1.band == 10_000))
    band_24g = Enum.filter(dataset, &(&1.band == 24_000))

    for {band_data, label} <- [{band_10g, "10 GHz"}, {band_24g, "24 GHz"}] do
      next_if_empty(band_data, label, fn ->
        IO.puts("--- #{label} Factor Breakpoints ---\n")

        # Refractivity gradient bins
        IO.puts("Refractivity Gradient → Median Distance:")
        print_binned(band_data, :avg_min_refractivity_gradient, :distance_km,
          [{-999, -200}, {-200, -150}, {-150, -100}, {-100, -75}, {-75, -55}, {-55, -40}, {-40, 0}])

        # Temperature bins
        IO.puts("\nSurface Temperature (C) → Median Distance:")
        print_binned(band_data, :avg_surface_temp_c, :distance_km,
          [{-20, 0}, {0, 10}, {10, 20}, {20, 25}, {25, 30}, {30, 35}, {35, 50}])

        # HPBL bins
        IO.puts("\nBoundary Layer Depth (m) → Median Distance:")
        print_binned(band_data, :avg_hpbl_m, :distance_km,
          [{0, 200}, {200, 500}, {500, 1000}, {1000, 1500}, {1500, 2000}, {2000, 5000}])

        # Pressure bins
        IO.puts("\nPressure (mb) → Median Distance:")
        print_binned(band_data, :avg_surface_pressure_mb, :distance_km,
          [{980, 1000}, {1000, 1010}, {1010, 1015}, {1015, 1020}, {1020, 1025}, {1025, 1040}])

        # PWAT bins
        IO.puts("\nPWAT (mm) → Median Distance:")
        print_binned(band_data, :avg_pwat_mm, :distance_km,
          [{0, 10}, {10, 20}, {20, 30}, {30, 40}, {40, 50}, {50, 80}])

        # Time of day
        IO.puts("\nUTC Hour → Median Distance:")
        for hour_range <- [{0, 3}, {3, 6}, {6, 9}, {9, 12}, {12, 15}, {15, 18}, {18, 21}, {21, 24}] do
          {lo, hi} = hour_range
          in_bin = Enum.filter(band_data, fn r ->
            r.utc_hour >= lo and r.utc_hour < hi
          end)
          print_bin_stats("  #{lo}-#{hi} UTC", in_bin, :distance_km)
        end

        # Month
        IO.puts("\nMonth → Median Distance:")
        for m <- 1..12 do
          in_bin = Enum.filter(band_data, &(&1.month == m))
          month_name = Enum.at(~w(Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec), m - 1)
          print_bin_stats("  #{month_name}", in_bin, :distance_km)
        end

        # Terrain verdict
        IO.puts("\nTerrain Verdict → Median Distance:")
        for verdict <- ["BLOCKED", "CLEAR", "FRESNEL_PARTIAL", nil] do
          in_bin = Enum.filter(band_data, &(&1.terrain_verdict == verdict))
          print_bin_stats("  #{verdict || "UNKNOWN"}", in_bin, :distance_km)
        end

        IO.puts("")
      end)
    end
  end

  # --- Interaction effects ---

  defp run_interaction_analysis(dataset) do
    band_10g = Enum.filter(dataset, &(&1.band == 10_000))

    next_if_empty(band_10g, "10 GHz interactions", fn ->
      IO.puts("--- 10 GHz: Gradient × Time of Day ---")
      for hour_range <- [{0, 6}, {6, 12}, {12, 18}, {18, 24}] do
        {lo, hi} = hour_range
        time_data = Enum.filter(band_10g, fn r -> r.utc_hour >= lo and r.utc_hour < hi end)

        strong = Enum.filter(time_data, fn r ->
          r.avg_min_refractivity_gradient != nil and r.avg_min_refractivity_gradient < -100
        end)
        weak = Enum.filter(time_data, fn r ->
          r.avg_min_refractivity_gradient != nil and r.avg_min_refractivity_gradient >= -100
        end)

        strong_med = median(Enum.map(strong, & &1.distance_km))
        weak_med = median(Enum.map(weak, & &1.distance_km))

        IO.puts("  #{lo}-#{hi} UTC: strong gradient (<-100) median=#{format_km(strong_med)} (n=#{length(strong)}), " <>
                "weak (>=-100) median=#{format_km(weak_med)} (n=#{length(weak)})")
      end

      IO.puts("\n--- 10 GHz: HPBL × Month ---")
      for month_group <- [{[6, 7, 8], "Summer"}, {[12, 1, 2], "Winter"}, {[3, 4, 5], "Spring"}, {[9, 10, 11], "Fall"}] do
        {months, label} = month_group
        seasonal = Enum.filter(band_10g, fn r -> r.month in months end)

        shallow = Enum.filter(seasonal, fn r -> r.avg_hpbl_m != nil and r.avg_hpbl_m < 500 end)
        deep = Enum.filter(seasonal, fn r -> r.avg_hpbl_m != nil and r.avg_hpbl_m >= 1000 end)

        shallow_med = median(Enum.map(shallow, & &1.distance_km))
        deep_med = median(Enum.map(deep, & &1.distance_km))

        IO.puts("  #{label}: shallow BL (<500m) median=#{format_km(shallow_med)} (n=#{length(shallow)}), " <>
                "deep BL (>=1000m) median=#{format_km(deep_med)} (n=#{length(deep)})")
      end

      IO.puts("\n--- 10 GHz: Ducting Detection vs Distance ---")
      ducting = Enum.filter(band_10g, & &1.ducting_either)
      no_ducting = Enum.filter(band_10g, &(!&1.ducting_either))
      IO.puts("  Ducting detected: median=#{format_km(median(Enum.map(ducting, & &1.distance_km)))} (n=#{length(ducting)})")
      IO.puts("  No ducting:       median=#{format_km(median(Enum.map(no_ducting, & &1.distance_km)))} (n=#{length(no_ducting)})")
    end)
  end

  # --- Statistical helpers ---

  defp spearman_correlation(xs, ys) do
    xs_clean = Enum.zip(xs, ys) |> Enum.reject(fn {x, _} -> is_nil(x) end)
    if length(xs_clean) < 10, do: nil, else: do_spearman(xs_clean)
  end

  defp do_spearman(pairs) do
    n = length(pairs)
    {xs, ys} = Enum.unzip(pairs)
    rx = rank(xs)
    ry = rank(ys)
    d_sq = Enum.zip(rx, ry) |> Enum.map(fn {a, b} -> (a - b) * (a - b) end) |> Enum.sum()
    1 - 6 * d_sq / (n * (n * n - 1))
  end

  defp rank(values) do
    indexed = values |> Enum.with_index() |> Enum.sort_by(fn {v, _i} -> v end)
    ranked = indexed |> Enum.with_index(1) |> Enum.map(fn {{_v, orig_i}, rank} -> {orig_i, rank} end)
    ranked |> Enum.sort_by(fn {orig_i, _rank} -> orig_i end) |> Enum.map(fn {_i, r} -> r * 1.0 end)
  end

  defp median([]), do: nil
  defp median(list) do
    sorted = Enum.sort(list)
    n = length(sorted)
    mid = div(n, 2)
    if rem(n, 2) == 0 do
      (Enum.at(sorted, mid - 1) + Enum.at(sorted, mid)) / 2
    else
      Enum.at(sorted, mid)
    end
  end

  defp percentile([], _p), do: nil
  defp percentile(list, p) do
    sorted = Enum.sort(list)
    k = (length(sorted) - 1) * p / 100
    f = trunc(k)
    c = Float.ceil(k) |> trunc()
    if f == c, do: Enum.at(sorted, f), else: Enum.at(sorted, f) + (k - f) * (Enum.at(sorted, c) - Enum.at(sorted, f))
  end

  defp print_binned(data, group_key, value_key, bins) do
    for {lo, hi} <- bins do
      in_bin = Enum.filter(data, fn row ->
        v = Map.get(row, group_key)
        v != nil and v >= lo and v < hi
      end)
      label = "  [#{lo}, #{hi})"
      print_bin_stats(String.pad_trailing(label, 18), in_bin, value_key)
    end
  end

  defp print_bin_stats(label, data, value_key) do
    n = length(data)
    if n > 0 do
      values = Enum.map(data, &Map.get(&1, value_key))
      med = median(values)
      p25 = percentile(values, 25)
      p75 = percentile(values, 75)
      IO.puts("#{label}  n=#{String.pad_leading("#{n}", 6)}  median=#{format_km(med)}  p25=#{format_km(p25)}  p75=#{format_km(p75)}")
    else
      IO.puts("#{label}  n=     0")
    end
  end

  defp next_if_empty([], label, _fun), do: IO.puts("Skipping #{label}: no data")
  defp next_if_empty(_data, _label, fun), do: fun.()

  defp format_corr(nil), do: "   N/A"
  defp format_corr(corr), do: :io_lib.format("~7.4f", [corr]) |> to_string()

  defp format_km(nil), do: "  N/A"
  defp format_km(km), do: :io_lib.format("~7.1f km", [km]) |> to_string()

  defp correlation_bar(nil), do: ""
  defp correlation_bar(corr) do
    len = round(abs(corr) * 20)
    bar = String.duplicate(if(corr >= 0, do: "+", else: "-"), len)
    "|#{bar}|"
  end
end
```

**Step 5: Run test to verify it passes**

Run: `mix test test/mix/tasks/propagation_analyze_test.exs --trace`
Expected: PASS

**Step 6: Run the analysis against real data**

Run: `mix propagation.analyze 2>&1 | tee docs/analysis_output.txt`

This will take several minutes (joining 58K QSOs against 54M HRRR profiles). Save the full output for reference during algo.md updates.

**Step 7: Commit**

```bash
git add lib/mix/tasks/propagation_analyze.ex test/mix/tasks/propagation_analyze_test.exs
git commit -m "Add mix propagation.analyze task for QSO-HRRR correlation analysis"
```

---

### Task 2: Interpret Analysis & Update algo.md

**Files:**
- Modify: `algo.md`

**Step 1: Read the analysis output**

Read `docs/analysis_output.txt` and identify:
- Which factors have strong vs weak correlation with distance
- Where current scoring thresholds diverge from data-suggested breakpoints
- Any interaction effects that the current independent-factor model misses
- Whether any current factors should be removed or new ones added

**Step 2: Update algo.md Part 2 (Key Empirical Findings)**

Add a new section "Data-Driven Refinements (April 2026)" documenting:
- Per-factor correlation strengths by band
- Revised threshold curves with data justification
- Weight adjustments with before/after comparison
- Any added or removed factors

**Step 3: Update algo.md Part 4 (Scoring Functions)**

Revise each factor's documentation to match new thresholds and behavior.

**Step 4: Update algo.md weights table**

Show old vs new weights with justification.

**Step 5: Commit**

```bash
git add algo.md
git commit -m "Update algo.md with data-driven findings from 58K QSO analysis"
```

---

### Task 3: Update Scorer & BandConfig

**Files:**
- Modify: `lib/microwaveprop/propagation/scorer.ex`
- Modify: `lib/microwaveprop/propagation/band_config.ex`
- Modify: `test/microwaveprop/propagation/scorer_test.exs`
- Modify: `test/microwaveprop/propagation/band_config_test.exs`

**Step 1: Update band_config.ex weights**

Change `@weights` map to match the data-derived optimal weights from the analysis.

**Step 2: Update band_config.ex thresholds**

Update `@refractivity_thresholds`, `@humidity_beneficial_thresholds`, seasonal tables, and any other thresholds that the analysis showed should change.

**Step 3: Update scorer.ex scoring functions**

Revise scoring function breakpoints to match the data-derived natural breakpoints. If the analysis warrants adding or removing factors, modify `composite_score/2` and the weights map accordingly.

**Step 4: Update tests to match new behavior**

Update `scorer_test.exs` and `band_config_test.exs` assertions to match the new thresholds and weights. Keep the same test structure — just adjust expected values.

**Step 5: Run tests**

Run: `mix test test/microwaveprop/propagation/scorer_test.exs test/microwaveprop/propagation/band_config_test.exs --trace`
Expected: PASS

**Step 6: Run full test suite**

Run: `mix test`
Expected: All pass

**Step 7: Commit**

```bash
git add lib/microwaveprop/propagation/scorer.ex lib/microwaveprop/propagation/band_config.ex
git add test/microwaveprop/propagation/scorer_test.exs test/microwaveprop/propagation/band_config_test.exs
git commit -m "Update scorer thresholds and weights from data analysis"
```

---

### Task 4: Training Mix Task

**Files:**
- Create: `lib/mix/tasks/propagation_train.ex`
- Modify: `lib/microwaveprop/propagation/model.ex` (add train/2, evaluate/2)
- Test: `test/mix/tasks/propagation_train_test.exs`
- Modify: `test/microwaveprop/propagation/model_test.exs`

**Step 1: Write failing test for Model.train/2**

```elixir
# In test/microwaveprop/propagation/model_test.exs, add:

describe "train/2" do
  test "trains model and returns params with reduced loss" do
    # Generate synthetic training data: 100 samples
    features = Nx.random_uniform({100, 13}, type: :f32)
    targets = Nx.random_uniform({100, 1}, type: :f32)

    {params, metrics} = Model.train(features, targets, epochs: 5, batch_size: 32)

    # Params should have the right structure
    assert Map.has_key?(params, "hidden_1")
    assert Map.has_key?(params, "hidden_2")
    assert Map.has_key?(params, "output")

    # Should return training metrics
    assert is_float(metrics.final_loss)
    assert metrics.final_loss >= 0
  end
end

describe "evaluate/2" do
  test "returns RMSE and R-squared on test data" do
    params = Model.init()
    features = Nx.random_uniform({50, 13}, type: :f32)
    targets = Nx.random_uniform({50, 1}, type: :f32)

    metrics = Model.evaluate(params, features, targets)

    assert is_float(metrics.rmse)
    assert is_float(metrics.r_squared)
    assert metrics.rmse >= 0
  end
end
```

**Step 2: Run test to verify it fails**

Run: `mix test test/microwaveprop/propagation/model_test.exs --trace`
Expected: FAIL — train/2 and evaluate/2 not defined

**Step 3: Implement Model.train/2 and Model.evaluate/2**

Add to `lib/microwaveprop/propagation/model.ex`:

```elixir
@doc """
Trains the model on the given features and targets tensors.

Options:
  - :epochs — number of training epochs (default 50)
  - :batch_size — samples per batch (default 256)
  - :learning_rate — Adam learning rate (default 0.001)
  - :patience — early stopping patience (default 5)

Returns {trained_params, %{final_loss: float}}.
"""
def train(features, targets, opts \\ []) do
  epochs = Keyword.get(opts, :epochs, 50)
  batch_size = Keyword.get(opts, :batch_size, 256)
  lr = Keyword.get(opts, :learning_rate, 0.001)

  model = build()

  loop =
    model
    |> Axon.Loop.trainer(:mean_squared_error, Polaris.Optimizers.adam(learning_rate: lr))
    |> Axon.Loop.metric(:mean_absolute_error)

  data =
    features
    |> Nx.to_batched(batch_size)
    |> Stream.zip(Nx.to_batched(targets, batch_size))
    |> Stream.map(fn {x, y} -> {%{"features" => x}, y} end)

  params = Axon.Loop.run(loop, data, Axon.ModelState.empty(),
    epochs: epochs,
    compiler: EXLA
  )

  # Compute final loss
  {_init, predict_fn} = Axon.build(model)
  preds = predict_fn.(params, %{"features" => features})
  final_loss = Nx.mean(Nx.pow(Nx.subtract(preds, targets), 2)) |> Nx.to_number()

  {params, %{final_loss: final_loss}}
end

@doc """
Evaluates model on test data. Returns %{rmse: float, r_squared: float}.
"""
def evaluate(params, features, targets) do
  model = build()
  {_init, predict_fn} = Axon.build(model)
  preds = predict_fn.(params, %{"features" => features})

  mse = Nx.mean(Nx.pow(Nx.subtract(preds, targets), 2)) |> Nx.to_number()
  rmse = :math.sqrt(mse)

  # R-squared
  ss_res = Nx.sum(Nx.pow(Nx.subtract(targets, preds), 2)) |> Nx.to_number()
  mean_y = Nx.mean(targets) |> Nx.to_number()
  ss_tot = Nx.sum(Nx.pow(Nx.subtract(targets, mean_y), 2)) |> Nx.to_number()
  r_squared = if ss_tot > 0, do: 1.0 - ss_res / ss_tot, else: 0.0

  %{rmse: rmse, r_squared: r_squared}
end
```

**Step 4: Run model tests**

Run: `mix test test/microwaveprop/propagation/model_test.exs --trace`
Expected: PASS

**Step 5: Write the training mix task**

```elixir
# lib/mix/tasks/propagation_train.ex
defmodule Mix.Tasks.PropagationTrain do
  @shortdoc "Train ML model from propagation scores + HRRR data"
  @moduledoc """
  Builds training data from propagation_scores joined to hrrr_profiles,
  trains the Axon model, evaluates on held-out test set, and saves weights.

  ## Usage

      mix propagation.train
      mix propagation.train --epochs 100 --batch-size 512
  """

  use Mix.Task

  alias Microwaveprop.Propagation.Model
  alias Microwaveprop.Repo

  @impl Mix.Task
  def run(args) do
    {opts, _, _} = OptionParser.parse(args,
      strict: [epochs: :integer, batch_size: :integer, sample: :integer])

    Application.put_env(:microwaveprop, Oban, queues: false)
    Mix.Task.run("app.start")

    epochs = Keyword.get(opts, :epochs, 50)
    batch_size = Keyword.get(opts, :batch_size, 256)
    sample_size = Keyword.get(opts, :sample, 500_000)

    IO.puts("Loading training data (sample=#{sample_size})...")
    {features, targets, band_counts} = load_training_data(sample_size)

    n = Nx.axis_size(features, 0)
    IO.puts("Loaded #{n} samples")
    for {band, count} <- Enum.sort(band_counts), do: IO.puts("  #{div(band, 1000)} GHz: #{count}")

    # 80/10/10 split
    n_train = round(n * 0.8)
    n_val = round(n * 0.1)

    train_x = Nx.slice(features, [0, 0], [n_train, 13])
    train_y = Nx.slice(targets, [0, 0], [n_train, 1])
    val_x = Nx.slice(features, [n_train, 0], [n_val, 13])
    val_y = Nx.slice(targets, [n_train, 0], [n_val, 1])
    test_x = Nx.slice(features, [n_train + n_val, 0], [n - n_train - n_val, 13])
    test_y = Nx.slice(targets, [n_train + n_val, 0], [n - n_train - n_val, 1])

    IO.puts("\nSplit: train=#{n_train}, val=#{n_val}, test=#{n - n_train - n_val}")
    IO.puts("Training for #{epochs} epochs, batch_size=#{batch_size}...\n")

    {params, train_metrics} = Model.train(train_x, train_y,
      epochs: epochs, batch_size: batch_size)

    IO.puts("\nTraining complete. Final loss: #{Float.round(train_metrics.final_loss, 6)}")

    IO.puts("\n=== Evaluation ===")
    val_metrics = Model.evaluate(params, val_x, val_y)
    IO.puts("Validation: RMSE=#{Float.round(val_metrics.rmse * 100, 2)} points, R²=#{Float.round(val_metrics.r_squared, 4)}")

    test_metrics = Model.evaluate(params, test_x, test_y)
    IO.puts("Test:       RMSE=#{Float.round(test_metrics.rmse * 100, 2)} points, R²=#{Float.round(test_metrics.r_squared, 4)}")

    IO.puts("\nSaving model to priv/models/propagation_v1.nx...")
    Model.save(params)
    IO.puts("Done!")
  end

  defp load_training_data(sample_size) do
    query = """
    SELECT
      h.surface_temp_c,
      h.surface_dewpoint_c,
      h.surface_pressure_mb,
      h.min_refractivity_gradient,
      h.hpbl_m,
      h.pwat_mm,
      EXTRACT(HOUR FROM ps.valid_time)::integer AS utc_hour,
      EXTRACT(MONTH FROM ps.valid_time)::integer AS month,
      ps.band_mhz,
      ps.score
    FROM propagation_scores ps
    JOIN hrrr_profiles h
      ON h.lat = ps.lat AND h.lon = ps.lon AND h.valid_time = ps.valid_time
    WHERE h.surface_temp_c IS NOT NULL
      AND h.surface_dewpoint_c IS NOT NULL
      AND h.min_refractivity_gradient IS NOT NULL
    ORDER BY RANDOM()
    LIMIT $1
    """

    result = Repo.query!(query, [sample_size], timeout: 600_000)

    band_counts = result.rows
    |> Enum.frequencies_by(fn row -> Enum.at(row, 8) end)

    {feature_rows, target_rows} =
      result.rows
      |> Enum.map(fn [temp, dewpoint, pressure, gradient, hpbl, pwat, hour, month, band_mhz, score] ->
        features = Model.encode_features(%{
          surface_temp_c: temp,
          surface_dewpoint_c: dewpoint,
          surface_pressure_mb: pressure,
          min_refractivity_gradient: gradient,
          hpbl_m: hpbl || 500.0,
          pwat_mm: pwat || 20.0,
          utc_hour: hour,
          month: month,
          freq_mhz: band_mhz
        })
        target = score / 100.0
        {features, [target]}
      end)
      |> Enum.unzip()

    features = Nx.tensor(feature_rows, type: :f32)
    targets = Nx.tensor(target_rows, type: :f32)

    {features, targets, band_counts}
  end
end
```

**Step 6: Run the training**

Run: `mix propagation.train --epochs 50 --sample 500000 2>&1 | tee docs/training_output.txt`

**Step 7: Commit**

```bash
git add lib/mix/tasks/propagation_train.ex lib/microwaveprop/propagation/model.ex
git add test/mix/tasks/propagation_train_test.exs test/microwaveprop/propagation/model_test.exs
git commit -m "Add ML training pipeline with Axon for propagation prediction"
```

---

### Task 5: Integrate ML Model into Grid Worker

**Files:**
- Modify: `lib/microwaveprop/propagation.ex` (add ML prediction path)
- Modify: `lib/microwaveprop/propagation/model.ex` (add predict_score/2)
- Modify: `test/microwaveprop/propagation_test.exs`
- Modify: `test/microwaveprop/propagation/model_test.exs`

**Step 1: Write failing test for Model.predict_score/2**

```elixir
# In model_test.exs
describe "predict_score/2" do
  test "returns integer score 0-100 from conditions map" do
    params = Model.init()  # random weights, but should still return valid range
    conditions = %{
      surface_temp_c: 25.0,
      surface_dewpoint_c: 15.0,
      surface_pressure_mb: 1013.0,
      min_refractivity_gradient: -80.0,
      hpbl_m: 500.0,
      pwat_mm: 25.0,
      utc_hour: 12,
      month: 6,
      freq_mhz: 10_000
    }

    score = Model.predict_score(params, conditions)
    assert is_integer(score)
    assert score >= 0 and score <= 100
  end
end
```

**Step 2: Run test to verify it fails**

Run: `mix test test/microwaveprop/propagation/model_test.exs --trace`
Expected: FAIL — predict_score/2 not defined

**Step 3: Implement Model.predict_score/2**

```elixir
@doc """
Predicts a 0-100 propagation score from a conditions map.
Convenience wrapper around encode_features + predict.
"""
def predict_score(params, conditions) do
  features =
    conditions
    |> encode_features()
    |> Nx.tensor(type: :f32)
    |> Nx.reshape({1, @feature_count})

  params
  |> predict(features)
  |> Nx.squeeze()
  |> Nx.multiply(100)
  |> Nx.round()
  |> Nx.to_number()
  |> trunc()
  |> max(0)
  |> min(100)
end
```

**Step 4: Run test**

Run: `mix test test/microwaveprop/propagation/model_test.exs --trace`
Expected: PASS

**Step 5: Add ML path to Propagation.score_grid_point_with_data/5**

Modify `lib/microwaveprop/propagation.ex` to try ML prediction first, fall back to algorithm:

```elixir
# In score_grid_point_with_data/5, after building conditions map:
# Try ML model if loaded, fall back to algorithm scorer
for band_config <- BandConfig.all_bands() do
  result = case ml_params() do
    nil ->
      Scorer.composite_score(conditions, band_config)
    params ->
      ml_conditions = Map.merge(conditions, %{freq_mhz: band_config.freq_mhz})
      score = Model.predict_score(params, ml_conditions)
      %{score: score, factors: %{ml_predicted: true}}
  end

  Map.put(result, :band_mhz, band_config.freq_mhz)
end
```

With a module-level cached model load:

```elixir
@ml_params_key :propagation_ml_params

def load_ml_model do
  case Model.load() do
    {:ok, params} ->
      :persistent_term.put(@ml_params_key, params)
      :ok
    :error ->
      :ok
  end
end

defp ml_params do
  try do
    :persistent_term.get(@ml_params_key)
  rescue
    ArgumentError -> nil
  end
end
```

**Step 6: Update Propagation tests**

Add tests verifying:
- Without ML model loaded, score_grid_point uses algorithm (existing behavior)
- With ML model loaded, score_grid_point uses ML predictions

**Step 7: Run full test suite**

Run: `mix test`
Expected: All pass

**Step 8: Commit**

```bash
git add lib/microwaveprop/propagation.ex lib/microwaveprop/propagation/model.ex
git add test/microwaveprop/propagation_test.exs test/microwaveprop/propagation/model_test.exs
git commit -m "Integrate ML model into grid worker with algorithm fallback"
```

---

### Task 6: Load ML Model at Application Startup

**Files:**
- Modify: `lib/microwaveprop/application.ex`

**Step 1: Add ML model loading to application start**

After Repo and other services start, call `Propagation.load_ml_model()` to cache params in persistent_term. This is a no-op if the model file doesn't exist.

**Step 2: Run full test suite**

Run: `mix test`
Expected: All pass

**Step 3: Run precommit**

Run: `mix precommit`
Expected: All pass

**Step 4: Commit**

```bash
git add lib/microwaveprop/application.ex
git commit -m "Load ML model at application startup"
```