R: Abstract Terminator Class

Terminator {bbotk} | R Documentation

## Abstract Terminator Class

### Description

Abstract `Terminator` class that implements the base functionality each terminator must provide. A terminator is an object that determines when to stop the optimization.

Termination of optimization works as follows:

- Evaluations in a instance are performed in batches.

- Before each batch evaluation, the Terminator is checked, and if it is positive, we stop.

- The optimization algorithm itself might decide not to produce any more points, or even might decide to do a smaller batch in its last evaluation.

Therefore the following note seems in order: While it is definitely possible to execute a fine-grained control for termination, and for many optimization algorithms we can specify exactly when to stop, it might happen that too few or even too many evaluations are performed, especially if multiple points are evaluated in a single batch (c.f. batch size parameter of many optimization algorithms). So it is advised to check the size of the returned archive, in particular if you are benchmarking multiple optimization algorithms.

### Technical details

`Terminator` subclasses can overwrite `.status()` to support progress bars via the package progressr. The method must return the maximum number of steps (`max_steps`) and the currently achieved number of steps (`current_steps`) as a named integer vector.

### Public fields

`param_set`

  paradox::ParamSet
  Set of control parameters for terminator.

`properties`

  (`character()`)
  Set of properties.

`unit`

  (`character()`)
  Unit of steps.

### Methods

#### Public methods

- `Terminator$new()`

- `Terminator$format()`

- `Terminator$print()`

- `Terminator$status()`

- `Terminator$remaining_time()`

- `Terminator$clone()`

#### Method `new()`

Creates a new instance of this R6 class.

##### Usage

    Terminator$new(param_set = ps(), properties = character())

##### Arguments

`param_set`

  (paradox::ParamSet)
  Set of control parameters for terminator.

`properties`

  (`character()`)
  Set of properties.

#### Method `format()`

Helper for print outputs.

##### Usage

    Terminator$format(with_params = FALSE)

##### Arguments

`with_params`

  (`logical(1)`)
  Add parameter values to format string.

#### Method `print()`

Printer.

##### Usage

    Terminator$print(...)

##### Arguments

`...`

  (ignored).

#### Method `status()`

Returns how many progression steps are made (`current_steps`) and the amount steps needed for termination (`max_steps`).

##### Usage

    Terminator$status(archive)

##### Arguments

`archive`

  (Archive).

##### Returns

named `integer(2)`.

#### Method `remaining_time()`

Returns remaining runtime in seconds. If the terminator is not time-based, the reaming runtime is `Inf`.

##### Usage

    Terminator$remaining_time(archive)

##### Arguments

`archive`

  (Archive).

##### Returns

`integer(1)`.

#### Method `clone()`

The objects of this class are cloneable with this method.

##### Usage

    Terminator$clone(deep = FALSE)

##### Arguments

`deep`

  Whether to make a deep clone.

### See Also

Other Terminator: `mlr_terminators_clock_time`, `mlr_terminators_combo`, `mlr_terminators_evals`, `mlr_terminators_none`, `mlr_terminators_perf_reached`, `mlr_terminators_run_time`, `mlr_terminators_stagnation_batch`, `mlr_terminators_stagnation`, `mlr_terminators`

[Package bbotk version 0.5.0 Index]