StepChoosers::ErrorControl< StepChooserUse, EvolvedVariableTag, ErrorControlSelector > Class Template Reference

Sets a goal based on time-stepper truncation error. More...

#include <ErrorControl.hpp>

Classes
struct	AbsoluteTolerance
struct	MaxFactor
struct	MinFactor
struct	RelativeTolerance
struct	SafetyFactor

Public Types
using	options = implementation defined
using	simple_tags = implementation defined
using	compute_tags = implementation defined
using	argument_tags = implementation defined

Public Member Functions
	ErrorControl (const double absolute_tolerance, const double relative_tolerance, const double max_factor, const double min_factor, const double safety_factor)
TimeStepRequest	operator() (const typename ::Tags::StepperErrors< EvolvedVariableTag >::type &errors, const double) const
bool	uses_local_data () const override
	Whether the result can differ on different elements, so requiring communication to synchronize the result across the domain. This is ignored for LTS step changing. More...
bool	can_be_delayed () const override
	Whether the result can be applied with a delay. More...
StepperErrorTolerances	tolerances () const override
void	pup (PUP::er &p) override
Public Member Functions inherited from StepChooser< StepChooserUse >
	WRAPPED_PUPable_abstract (StepChooser)
virtual bool	uses_local_data () const =0
	Whether the result can differ on different elements, so requiring communication to synchronize the result across the domain. This is ignored for LTS step changing. More...
virtual bool	can_be_delayed () const =0
	Whether the result can be applied with a delay. More...
template<typename StepChoosersToUse = AllStepChoosers, typename DbTags >
TimeStepRequest	desired_step (const double last_step, const db::DataBox< DbTags > &box) const
	The last_step parameter describes the step size to be adjusted. It may be the step size or the slab size, or may be infinite if the appropriate size cannot be determined. More...

Static Public Member Functions
static std::string	name ()

Static Public Attributes
static constexpr Options::String	help

Detailed Description

template<typename StepChooserUse, typename EvolvedVariableTag, typename ErrorControlSelector = NoSuchType>
class StepChoosers::ErrorControl< StepChooserUse, EvolvedVariableTag, ErrorControlSelector >

Sets a goal based on time-stepper truncation error.

Details

The suggested step is calculated via a simple specialization of the scheme suggested in [87]. We first compute the aggregated error measure from the stepper error:

$$E=\underset{i}{max}(|E_i|/s{c}_i),$$

where $E_i$ is the ODE error reported for each individual grid point, reported by the time stepper, and $s{c}_i$ is the step control measure determined by the tolerances:

$$s{c}_i=Ato{l}_i+max(|y_i|,|y_i+E_i|)Rto{l}_i,$$

and $y_i$ is the value of the function at the previous step at grid point $i$. (The estimate is more commonly done comparing with the current step, but using the previous step avoids a memory allocation in the TimeStepper and should not have a major effect on the result.)

When choosing a step size for LTS or when no record of previous error is available, the step has size:

$$h_{\text{new}}=h\cdot min(F_{\text{max}},max(F_{\text{min}},\frac{F_{\text{safety}}}{E^{1/(q+1)}})),$$

where $h_{\text{new}}$ is the new suggested step size $h$ is the previous step size, $F_{\text{max}}$ is the maximum factor by which we allow the step to increase, $F_{\text{min}}$ is the minimum factor by which we allow the step to decrease. $F_{\text{safety}}$ is the safety factor on the computed error – this forces the step size slightly lower than we would naively compute so that the result of the step will likely be within the target error. $q$ is the order of the stepper error calculation. Intuitively, we should change the step less drastically for a higher order stepper.

When controlling slab size, after the first error calculation, the error $E$ is recorded in the DataBox, and subsequent error calculations use a simple PI scheme suggested in [166] section 17.2.1:

$$h_{\text{new}}=h\cdot min(F_{\text{max}},max(F_{\text{min}},F_{\text{safety}}{E}^{-0.7/(q+1)}{E}_{\text{prev}}^{0.4/(q+1)})),$$

where $E_{\text{prev}}$ is the error computed in the previous step. This method is never used for choosing an LTS step because the restriction of step size changes to factors of two was found to interfere with the more gradual increase chosen by the PI controller.

Note

The template parameter ErrorControlSelector is used to disambiguate in the input-file options between ErrorControl step choosers that are based on different variables. This is needed if multiple systems are evolved in the same executable. The name used for the input file includes ErrorControlSelector::name() if it is provided.

Member Function Documentation

can_be_delayed()

template<typename StepChooserUse , typename EvolvedVariableTag , typename ErrorControlSelector = NoSuchType>

bool StepChoosers::ErrorControl< StepChooserUse, EvolvedVariableTag, ErrorControlSelector >::can_be_delayed ( ) const

inlineoverridevirtual

Whether the result can be applied with a delay.

StepChoosers setting the .end or .end_hard_limit fields of TimeStepRequest must return false here.

Implements StepChooser< StepChooserUse >.

uses_local_data()

template<typename StepChooserUse , typename EvolvedVariableTag , typename ErrorControlSelector = NoSuchType>

bool StepChoosers::ErrorControl< StepChooserUse, EvolvedVariableTag, ErrorControlSelector >::uses_local_data ( ) const

inlineoverridevirtual

Whether the result can differ on different elements, so requiring communication to synchronize the result across the domain. This is ignored for LTS step changing.

Note

As this is only used for slab-size changing, the last_step passed to the call operator is not considered local data.

Implements StepChooser< StepChooserUse >.

Member Data Documentation

help

template<typename StepChooserUse , typename EvolvedVariableTag , typename ErrorControlSelector = NoSuchType>

constexpr Options::String StepChoosers::ErrorControl< StepChooserUse, EvolvedVariableTag, ErrorControlSelector >::help

staticconstexpr

Initial value:

{
      "Sets a goal based on time-stepper truncation error."}

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The documentation for this class was generated from the following file:

• src/Time/StepChoosers/ErrorControl.hpp