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# 3. Callbacks

Monitor and influence the optimization procedure via callbacks.

Callbacks are callables which are invoked after each iteration of the optimizer and are passed the results “so far”. Callbacks can monitor progress, or stop the optimization early by returning `True`.

## 3.1. Monitoring callbacks

- `VerboseCallback`

- `TimerCallback`

## 3.2. Early stopping callbacks

- `DeltaXStopper`

- `DeadlineStopper`

- `DeltaXStopper`

- `DeltaYStopper`

- `EarlyStopper`

## 3.3. Other callbacks

- `CheckpointSaver`