# The default algorithm options#

The order is the following:

1. Convergence and Stopping Criteria

2. Trust Region Parameters

3. Other Numerical Algorithm Group Tuning Parameters

estimagic.optimization.algo_options.CONVERGENCE_RELATIVE_CRITERION_TOLERANCE = 2e-09#

Stop when the relative improvement between two iterations is below this.

The exact definition of relative improvement depends on the optimizer and should be documented there. To disable it, set it to 0.

The default value is inspired by scipy L-BFGS-B defaults, but rounded.

Type

float

estimagic.optimization.algo_options.CONVERGENCE_ABSOLUTE_CRITERION_TOLERANCE = 0#

Stop when the absolute improvement between two iterations is below this.

Disabled by default because it is very problem specific.

Type

float

Stop when the gradient are smaller than this.

For some algorithms this criterion refers to all entries, for others to some norm.

For bound constrained optimizers this typically refers to a projected gradient. The exact definition should be documented for each optimizer.

The default is the same as scipy. To disable it, set it to zero.

Type

float

Stop when the gradient, divided by the absolute value of the criterion function is smaller than this. For some algorithms this criterion refers to all entries, for others to some norm.For bound constrained optimizers this typically refers to a projected gradient. The exact definition should be documented for each optimizer. To disable it, set it to zero.

Type

float

Stop when all entries (or for some algorithms the norm) of the gradient, divided by the norm of the gradient at start parameters is smaller than this. For bound constrained optimizers this typically refers to a projected gradient. The exact definition should be documented for each optimizer. To disable it, set it to zero.

Type

float

estimagic.optimization.algo_options.CONVERGENCE_RELATIVE_PARAMS_TOLERANCE = 1e-05#

Stop when the relative change in parameters is smaller than this. The exact definition of relative change and whether this refers to the maximum change or the average change depends on the algorithm and should be documented there. To disable it, set it to zero. The default is the same as in scipy.

Type

float

estimagic.optimization.algo_options.CONVERGENCE_ABSOLUTE_PARAMS_TOLERANCE = 0#

Stop when the absolute change in parameters between two iterations is smaller than this. Whether this refers to the maximum change or the average change depends on the algorithm and should be documented there.

Disabled by default because it is very problem specific. To enable it, set it to a value larger than zero.

Type

float

estimagic.optimization.algo_options.CONVERGENCE_NOISE_CORRECTED_CRITERION_TOLERANCE = 1.0#

Stop when the evaluations on the set of interpolation points all fall within this factor of the noise level. The default is 1, i.e. when all evaluations are within the noise level. If you want to not use this criterion but still flag your criterion function as noisy, set this tolerance to 0.0.

Warning

Very small values, as in most other tolerances don’t make sense here.

Type

float

Stop when the lower trust region radius falls below this value.

Type

float

estimagic.optimization.algo_options.STOPPING_MAX_CRITERION_EVALUATIONS = 1000000#

int: If the maximum number of function evaluation is reached, the optimization stops but we do not count this as successful convergence. The function evaluations used to evaluate a numerical gradient do not count for this.

estimagic.optimization.algo_options.STOPPING_MAX_CRITERION_EVALUATIONS_GLOBAL = 1000#

int: If the maximum number of function evaluation is reached, the optimization stops but we do not count this as successful convergence. The function evaluations used to evaluate a numerical gradient do not count for this. Set to a lower number than STOPPING_MAX_CRITERION_EVALUATIONS for global optimizers.

estimagic.optimization.algo_options.STOPPING_MAX_ITERATIONS = 1000000#

int: If the maximum number of iterations is reached, the optimization stops, but we do not count this as successful convergence. The difference to max_criterion_evaluations is that one iteration might need several criterion evaluations, for example in a line search or to determine if the trust region radius has to be shrunk.

estimagic.optimization.algo_options.CONVERGENCE_SECOND_BEST_ABSOLUTE_CRITERION_TOLERANCE = 1e-08#

absolute criterion tolerance estimagic requires if no other stopping criterion apart from max iterations etc. is available this is taken from scipy (SLSQP’s value, smaller than Nelder-Mead).

Type

float

estimagic.optimization.algo_options.CONVERGENCE_SECOND_BEST_ABSOLUTE_PARAMS_TOLERANCE = 1e-08#

The absolute parameter tolerance estimagic requires if no other stopping criterion apart from max iterations etc. is available. This is taken from pybobyqa.

Type

float

estimagic.optimization.algo_options.CONVERGENCE_SLOW_PROGRESS = {'comparison_period': 5, 'max_insufficient_improvements': None, 'threshold_to_characterize_as_slow': 1e-08}#

Specification of when to terminate or reset the optimization because of only slow improvements. This is similar to an absolute criterion tolerance only that instead of a single improvement the average over several iterations must be small.

Possible entries are:
threshold_to_characterize_as_slow (float): Threshold whether an improvement

is insufficient. Note: the improvement is divided by the comparison_period. So this is the required average improvement per iteration over the comparison period.

max_insufficient_improvements (int): Number of consecutive

insufficient improvements before termination (or reset). Default is 20 * len(x).

comparison_period (int):

How many iterations to go back to calculate the improvement. For example 5 would mean that each criterion evaluation is compared to the criterion value from 5 iterations before.

Type

dict

estimagic.optimization.algo_options.MAX_LINE_SEARCH_STEPS = 20#

Inspired by scipy L-BFGS-B.

Type

int

estimagic.optimization.algo_options.LIMITED_MEMORY_STORAGE_LENGTH = 10#

Taken from scipy L-BFGS-B.

Type

int

estimagic.optimization.algo_options.THRESHOLD_FOR_SAFETY_STEP = 0.5#

Threshold for when to call the safety step ($$\gamma_s$$).

$$\text{proposed step} \leq \text{threshold_for_safety_step} \cdot \text{current_lower_trustregion_radius}$$.

Type

float

estimagic.optimization.algo_options.CONSTRAINTS_ABSOLUTE_TOLERANCE = 1e-05#

Allowed tolerance of the equality and inequality constraints for values to be considered ‘feasible’.

Type

float

estimagic.optimization.algo_options.TRUSTREGION_THRESHOLD_SUCCESSFUL = 0.1#

Share of the predicted improvement that has to be achieved for a trust region iteration to count as successful.

Type

float

estimagic.optimization.algo_options.TRUSTREGION_THRESHOLD_VERY_SUCCESSFUL = 0.7#

Share of predicted improvement that has to be achieved for a trust region iteration to count as very successful.criterion_noisy

Type

float

estimagic.optimization.algo_options.TRUSTREGION_SHRINKING_FACTOR_NOT_SUCCESSFUL = None#

Ratio by which to shrink the upper trust region radius when realized improvement does not match the threshold_successful. The default is 0.98 if the criterion is noisy and 0.5 else.

Type

float

estimagic.optimization.algo_options.TRUSTREGION_EXPANSION_FACTOR_SUCCESSFUL = 2.0#

Ratio by which to expand the upper trust region radius $$\Delta_k$$ in very successful iterations ($$\gamma_{inc}$$ in the notation of the paper).

Type

float

estimagic.optimization.algo_options.TRUSTREGION_EXPANSION_FACTOR_VERY_SUCCESSFUL = 4.0#

Ratio of the proposed step ($|s_k|$) by which to expand the upper trust region radius ($$\Delta_k$$) in very successful iterations ($$\overline{\gamma}_{inc}$$ in the notation of the paper).

Type

float

Ratio by which to shrink the lower trust region radius ($$\rho_k$$) ($$\alpha_1$$ in the notation of the paper). Default is 0.9 if the criterion is noisy and 0.1 else.

Type

float

Ratio of the current lower trust region ($$\rho_k$$) by which to shrink the upper trust region radius ($$\Delta_k$$) when the lower one is shrunk ($$\alpha_2$$ in the notation of the paper). Default is 0.95 if the criterion is noisy and 0.5 else.

Type

float

estimagic.optimization.algo_options.INITIAL_DIRECTIONS = 'coordinate'#

How to draw the initial directions. Possible values are “coordinate” for coordinate directions (the default) or “random”.

Type

string

estimagic.optimization.algo_options.RANDOM_DIRECTIONS_ORTHOGONAL = True#

Whether to make randomly drawn initial directions orthogonal.

Type

bool

estimagic.optimization.algo_options.INTERPOLATION_ROUNDING_ERROR = 0.1#

Internally, all the NAG algorithms store interpolation points with respect to a base point $$x_b$$; that is, we store $$\{y_t-x_b\}$$, which reduces the risk of roundoff errors. We shift $$x_b$$ to $$x_k$$ when $$\text{proposed step} \leq \text{interpolation_rounding_error} \cdot \|x_k-x_b\|$$.

Type

float

estimagic.optimization.algo_options.CLIP_CRITERION_IF_OVERFLOWING = True#

Whether to clip the criterion to avoid OverflowError.

Type

bool

estimagic.optimization.algo_options.TRUSTREGION_PRECONDITION_INTERPOLATION = True#

whether to scale the interpolation linear system to improve conditioning.

Type

bool

estimagic.optimization.algo_options.RESET_OPTIONS = {'auto_detect': True, 'auto_detect_history': 30, 'auto_detect_min_correlations': 0.1, 'auto_detect_min_jacobian_increase': 0.015, 'max_consecutive_unsuccessful_resets': 10, 'max_interpolation_points': None, 'max_iterations_without_new_best_after_soft_reset': None, 'max_unsuccessful_resets': None, 'minimal_trustregion_radius_tolerance_scaling_at_reset': 1.0, 'move_center_at_soft_reset': True, 'n_additional_extra_points_to_replace_per_reset': 0, 'n_extra_interpolation_points_per_hard_reset': 0, 'n_extra_interpolation_points_per_soft_reset': 0, 'points_to_replace_at_soft_reset': 3, 'reset_type': 'soft', 'reuse_criterion_value_at_hard_reset': True, 'trust_region_scaling_at_unsuccessful_reset': None, 'use_resets': None}#

Options for reseting the optimization.

Possible entries are:

use_resets (bool): Whether to do resets when the lower trust

region radius ($$\rho_k$$) reaches the stopping criterion ($$\rho_{end}$$), or (optionally) when all interpolation points are within noise level. Default is True if the criterion is noisy.

which the trust region stopping criterion is multiplied at each reset.

reset_type (str): Whether to use “soft” or “hard” resets. Default is “soft”.

move_center_at_soft_reset (bool): Whether to move the trust region center

($x_k$) to the best new point evaluated in stead of keeping it constant.

points_to_replace_at_soft_reset (int): Number of interpolation points to move

at each soft reset.

reuse_criterion_value_at_hard_reset (bool): Whether or not to recycle the

criterion value at the best iterate found when performing a hard reset. This saves one criterion evaluation.

max_iterations_without_new_best_after_soft_reset (int):

The maximum number of successful steps in a given run where the new criterion value is worse than the best value found in previous runs before terminating. Default is max_criterion_evaluations.

auto_detect (bool): Whether or not to

automatically determine when to reset. This is an additional condition and resets can still be triggered by small upper trust region radius, etc. There are two criteria used: upper trust region radius shrinkage (no increases over the history, more decreases than no changes) and changes in the model Jacobian (consistently increasing trend as measured by slope and correlation coefficient of the line of best fit).

auto_detect_history (int):

How many iterations of model changes and trust region radii to store.

auto_detect_min_jacobian_increase (float):

Minimum rate of increase of the Jacobian over past iterations to cause a reset.

auto_detect_min_correlations (float):

Minimum correlation of the Jacobian data set required to cause a reset.

max_consecutive_unsuccessful_resets (int): maximum number of consecutive

unsuccessful resets allowed (i.e. resets which did not outperform the best known value from earlier runs).

Only used when using nag_bobyqa:

max_unsuccessful_resets (int):

number of total unsuccessful resets allowed. Default is 20 if seek_global_optimum and else unrestricted.

trust_region_scaling_at_unsuccessful_reset (float): Factor by which to

expand the initial lower trust region radius ($$\rho_{beg}$$) after unsuccessful resets. Default is 1.1 if seek_global_optimum else 1.

Only used when using nag_dfols:

max_interpolation_points (int): Maximum allowed value of the number of

interpolation points. This is useful if the number of interpolation points increases with each reset, e.g. when n_extra_interpolation_points_per_soft_reset > 0. The default is n_interpolation_points.

n_extra_interpolation_points_per_soft_reset (int): Number of points to add to

the interpolation set with each soft reset.

n_extra_interpolation_points_per_hard_reset (int): Number of points to add to

the interpolation set with each hard reset.

n_extra_points_to_replace_successful. With each reset n_extra_points_to_replace_successful is increased by this number.

Type

dict

estimagic.optimization.algo_options.TRUSTREGION_FAST_START_OPTIONS = {'floor_of_jacobian_singular_values': 1, 'full_geometry_improving_step': False, 'geometry_improving_steps': False, 'jacobian_max_condition_number': 100000000.0, 'method': 'auto', 'min_inital_points': None, 'n_extra_search_directions_per_iteration': 0, 'reset_min_trustregion_radius_after_fast_start': False, 'reset_trustregion_radius_after_fast_start': False, 'safety_steps': True, 'scale_of_jacobian_components_perturbation': 0.01, 'scale_of_trustregion_step_perturbation': None, 'shrink_upper_radius_in_safety_steps': False, 'shrinking_factor_not_successful': None}#

Options to start the optimization while building the full trust region model.

To activate this, set the number of interpolation points at which to evaluate the criterion before doing the first step, min_initial_points, to something smaller than the number of parameters.

The following options can be specified:

min_initial_points (int): Number of initial interpolation

points in addition to the start point. This should only be changed to a value less than len(x), and only if the default setup cost of len(x) + 1 evaluations of the criterion is impractical. If this is set to be less than the default, the input value of n_interpolation_points should be set to len(x). If the default is used, all the other parameters have no effect. Default is n_interpolation_points - 1. If the default setup costs of the evaluations are very large, DF-OLS can start with less than len(x) interpolation points and add points to the trust region model with every iteration.

method (“jacobian”, “trustregion” or “auto”):

When there are less interpolation points than len(x) the model is underdetermined. This can be fixed in two ways: If “jacobian”, the interpolated Jacobian is perturbed to have full rank, allowing the trust region step to include components in the full search space. This is the default if len(x) \geq number of root contributions. If “trustregion_step”, the trust region step is perturbed by an orthogonal direction not yet searched. It is the default if len(x) < number of root contributions.

scale_of_trustregion_step_perturbation (float):

When adding new search directions, the length of the step is the trust region radius multiplied by this value. The default is 0.1 if method == "trustregion" else 1.

scale_of_jacobian_components_perturbation (float): Magnitude of extra

components added to the Jacobian. Default is 1e-2.

floor_of_jacobian_singular_values (float): Floor singular

values of the Jacobian at this factor of the last non zero value. As of version 1.2.1 this option is not yet supported by DF-OLS!

scale_of_jacobian_singular_value_floor (float):

Floor singular values of the Jacobian at this factor of the last nonzero value.

jacobian_max_condition_number (float): Cap on the condition number

of Jacobian after applying floors to singular values (effectively another floor on the smallest singular value, since the largest singular value is fixed).

geometry_improving_steps (bool): Whether to do geometry-improving steps in the

trust region algorithm, as per the usual algorithm during the fast start.

safety_steps (bool):

Whether to perform safety steps.

shrink_upper_radius_in_safety_steps (bool): During the fast start whether to

shrink the upper trust region radius in safety steps.

full_geometry_improving_step (bool): During the fast start whether to do a

full geometry-improving step within safety steps (the same as the post fast start phase of the algorithm). Since this involves reducing the upper trust region radius, this can only be True if shrink_upper_radius_in_safety_steps == False.

Whether or not to reset the upper trust region radius to its initial value at the end of the fast start phase.

Whether or not to reset the minimum trust region radius ($$\rho_k$$) to its initial value at the end of the fast start phase.

shrinking_factor_not_successful (float):

Ratio by which to shrink the trust region radius when realized improvement does not match the threshold_for_successful_iteration during the fast start phase. By default it is the same as reduction_when_not_successful.

n_extra_search_directions_per_iteration (int): Number of new search

directions to add with each iteration where we do not have a full set of search directions. This approach is not recommended! Default is 0.

Type

dict