# C634 — Generate the full cross-rail matrix

## Question

Does one indexed formula account for all nine span comparisons?

## Inputs

```json
{
  "head_difference": 2366,
  "rail_step": 7,
  "indices": [
    0,
    1,
    2
  ]
}
```

## Sources

```json
[
  "File70 §§6.3,6.5; derived completion of source geometry"
]
```

## Opened utc

2026-09-28T00:57:07.226648+00:00

## Results

```json
{
  "span_matrix": [
    [
      2366,
      2373,
      2380
    ],
    [
      2359,
      2366,
      2373
    ],
    [
      2352,
      2359,
      2366
    ]
  ],
  "multiplicities": {
    "2352": 1,
    "2359": 2,
    "2366": 3,
    "2373": 2,
    "2380": 1
  },
  "formula": "D(i,j)=2366+7(j−i)",
  "source_selected_extremes": [
    2352,
    2366,
    2380
  ]
}
```

## Finding

The complete matrix has five span values with multiplicities1,2,3,2,1. Minimum, corresponding and maximum spans are2366−14,2366,2366+14; the other entries are generated comparisons, not additional source appointments.

## Reassessment

Explain the separate exposure span using its two thirteen-year flanks.

## Checks

```json
{
  "extremes": true,
  "frequency": true,
  "matrix_from_dates": true
}
```

## Closed utc

2026-09-28T00:57:07.226929+00:00

## Record provenance

Exact record hash: `3bef9066b0c13130bfd753799a43e2aaee36086aa9fcaf0f767da80df7c64879`

Source journal: `Research_Cycles/C0632_C0731/journal.json`