# Refinement

> USearch for C#

```csharp
RefineReport report = index.On(pool).Refine(expansionFactor: 256);
```

Refinement re-selects the neighbors of every stored entry against the finished graph, improving edges that were chosen when the graph around them was still incomplete.
It is a build step rather than a repair: a cheap insertion pass followed by one refinement reaches a better graph, in less total time, than a single expensive insertion pass, so a wide expansion factor belongs here rather than in `Insert`.
The return is a `RefineReport` of the nodes re-selected and `Changed`, the islands found and reconnected, and the `Reachability` audit closing the heal; `Changed` at zero means the graph has settled, so a caller under a time budget loops until it falls below whatever rate it considers settled.
Searches may run throughout.

### Absorbing & Splitting

```csharp
index.On(pool).Absorb(donor);
index.On(pool).Split([left, right], seed: 7); // two empty receivers take a part each
```

Bigger indexes come from absorbing, never mutating: `Absorb` appends each donor in turn, keeping its graph and linking it in across the appended part.
Every donor it absorbs is consumed and then refuses every verb with `Status.Uninitialized`, while one it did not absorb, like a donor of another scalar refused with `Status.ConfigMismatch`, stays a live index you still own, though its entries may already have moved.
`Split` is its inverse, partitioning the entries along the graph into empty receivers and leaving the source empty and live; both answer a `RefineReport` of their closing refinements.