oomph::EBDF3 Class Reference

#include <explicit_timesteppers.h>

Inheritance diagram for oomph::EBDF3:

Public Member Functions
	EBDF3 ()
	Constructor, set the type. More...
	EBDF3 (const EBDF3 &)=delete
	Broken copy constructor. More...
void	operator= (const EBDF3 &)=delete
	Broken assignment operator. More...
void	set_weights (const double &dtn, const double &dtnm1, const double &dtnm2)
	Calculate the weights for this set of step sizes. More...
void	timestep (ExplicitTimeSteppableObject *const &object_pt, const double &dt)
	Function that is used to advance the solution by time dt. More...
Public Member Functions inherited from oomph::ExplicitTimeStepper
	ExplicitTimeStepper ()
	Empty Constructor. More...
	ExplicitTimeStepper (const ExplicitTimeStepper &)=delete
	Broken copy constructor. More...
void	operator= (const ExplicitTimeStepper &)=delete
	Broken assignment operator. More...
virtual	~ExplicitTimeStepper ()
	Empty virtual destructor — no memory is allocated in this class. More...

Private Attributes
double	Yn_weight
double	Ynm1_weight
double	Ynm2_weight
double	Fn_weight

Additional Inherited Members
Protected Attributes inherited from oomph::ExplicitTimeStepper
std::string	Type

Detailed Description

=========================================================== An explicit version of BDF3 (i.e. uses derivative evaluation at y_n instead of y_{n+1}). Useful as a predictor because it is third order accurate but requires only one function evaluation (i.e. only one mass matrix inversion + residual calculation).

Constructor & Destructor Documentation

EBDF3() [1/2]

oomph::EBDF3::EBDF3 ( )

inline

Constructor, set the type.

{}

EBDF3() [2/2]

oomph::EBDF3::EBDF3 ( const EBDF3 &  )

delete

Broken copy constructor.

Member Function Documentation

operator=()

void oomph::EBDF3::operator= ( const EBDF3 &  )

delete

Broken assignment operator.

set_weights()

void oomph::EBDF3::set_weights	(	const double &	dtn,
		const double &	dtnm1,
		const double &	dtnm2
	)

Calculate the weights for this set of step sizes.

  {
    using namespace std;
 
    // If this is slow we can probably optimise by doing direct
    // multiplication instead of using pow.
 
    // Generated using sympy from my python ode code.
 
    double denom = pow(dtnm1, 4) * dtnm2 + 2 * pow(dtnm1, 3) * pow(dtnm2, 2) +
                   pow(dtnm1, 2) * pow(dtnm2, 3);
 
    Yn_weight =
      -(2 * pow(dtn, 3) * dtnm1 * dtnm2 + pow(dtn, 3) * pow(dtnm2, 2) +
        3 * pow(dtn, 2) * pow(dtnm1, 2) * dtnm2 +
        3 * pow(dtn, 2) * dtnm1 * pow(dtnm2, 2) + pow(dtn, 2) * pow(dtnm2, 3) -
        pow(dtnm1, 4) * dtnm2 - 2 * pow(dtnm1, 3) * pow(dtnm2, 2) -
        pow(dtnm1, 2) * pow(dtnm2, 3)) /
      denom;
 
    Ynm1_weight =
      -(-pow(dtn, 3) * pow(dtnm1, 2) - 2 * pow(dtn, 3) * dtnm1 * dtnm2 -
        pow(dtn, 3) * pow(dtnm2, 2) - pow(dtn, 2) * pow(dtnm1, 3) -
        3 * pow(dtn, 2) * pow(dtnm1, 2) * dtnm2 -
        3 * pow(dtn, 2) * dtnm1 * pow(dtnm2, 2) - pow(dtn, 2) * pow(dtnm2, 3)) /
      denom;
 
    Ynm2_weight =
      -(pow(dtn, 3) * pow(dtnm1, 2) + pow(dtn, 2) * pow(dtnm1, 3)) / denom;
 
    Fn_weight =
      -(-pow(dtn, 3) * pow(dtnm1, 2) * dtnm2 -
        pow(dtn, 3) * dtnm1 * pow(dtnm2, 2) -
        2 * pow(dtn, 2) * pow(dtnm1, 3) * dtnm2 -
        3 * pow(dtn, 2) * pow(dtnm1, 2) * pow(dtnm2, 2) -
        pow(dtn, 2) * dtnm1 * pow(dtnm2, 3) - dtn * pow(dtnm1, 4) * dtnm2 -
        2 * dtn * pow(dtnm1, 3) * pow(dtnm2, 2) -
        dtn * pow(dtnm1, 2) * pow(dtnm2, 3)) /
      denom;
  }

References Fn_weight, Eigen::bfloat16_impl::pow(), Yn_weight, Ynm1_weight, and Ynm2_weight.

Referenced by timestep().

timestep()

void oomph::EBDF3::timestep ( ExplicitTimeSteppableObject *const &  object_pt, const double &  dt  )

virtual

Function that is used to advance the solution by time dt.

Implements oomph::ExplicitTimeStepper.

  {
    using namespace StringConversion;
 
    object_pt->actions_before_explicit_timestep();
    object_pt->actions_before_explicit_stage();
 
    // Storage indicies for the history values that we need
    unsigned tn = 1;
    unsigned tnm1 = tn + 1;
    unsigned tnm2 = tnm1 + 1;
 
    // Check dts are the same, this will need to be removed if ebdf3 is being
    // used as something other than a predictor... But seeing as it isn't
    // stable that isn't likely.
#ifdef PARANOID
    if (std::abs(dt - object_pt->time_pt()->dt(0)) > 1e-15)
    {
      std::string err =
        "Inconsistent dts! Predictor is stepping by " + to_string(dt);
      err += " but dt(0) = " + to_string(object_pt->time_pt()->dt(0));
      throw OomphLibError(
        err, OOMPH_EXCEPTION_LOCATION, OOMPH_CURRENT_FUNCTION);
    }
#endif
 
    // Get older dt values
    double dtnm1 = object_pt->time_pt()->dt(1);
    double dtnm2 = object_pt->time_pt()->dt(2);
 
    // Calculate weights for these dts
    set_weights(dt, dtnm1, dtnm2);
 
    // Get derivative value at step n (even though this uses values from t=0 =
    // step n+1, it's ok because we haven't changed the values in that slot
    // yet).
    DoubleVector fn;
    object_pt->get_dvaluesdt(fn);
    fn *= Fn_weight;
 
    // Extract history values and multiply by their weights
    DoubleVector ynp1, yn, ynm1, ynm2;
    object_pt->get_dofs(tn, yn);
    yn *= Yn_weight;
    object_pt->get_dofs(tnm1, ynm1);
    ynm1 *= Ynm1_weight;
    object_pt->get_dofs(tnm2, ynm2);
    ynm2 *= Ynm2_weight;
 
 
    // Add everything together
    ynp1 = yn;
    ynp1 += ynm1;
    ynp1 += ynm2;
    ynp1 += fn;
 
    // Done, update things in the object
    object_pt->set_dofs(ynp1);
    object_pt->time() += dt;
 
    // Actions functions
    object_pt->actions_after_explicit_stage();
    object_pt->actions_after_explicit_timestep();
  }

References abs(), oomph::ExplicitTimeSteppableObject::actions_after_explicit_stage(), oomph::ExplicitTimeSteppableObject::actions_after_explicit_timestep(), oomph::ExplicitTimeSteppableObject::actions_before_explicit_stage(), oomph::ExplicitTimeSteppableObject::actions_before_explicit_timestep(), oomph::Time::dt(), e(), Fn_weight, oomph::ExplicitTimeSteppableObject::get_dofs(), oomph::ExplicitTimeSteppableObject::get_dvaluesdt(), OOMPH_CURRENT_FUNCTION, OOMPH_EXCEPTION_LOCATION, oomph::ExplicitTimeSteppableObject::set_dofs(), set_weights(), oomph::Global_string_for_annotation::string(), oomph::ExplicitTimeSteppableObject::time(), oomph::ExplicitTimeSteppableObject::time_pt(), oomph::StringConversion::to_string(), Yn_weight, Ynm1_weight, and Ynm2_weight.

Member Data Documentation

Fn_weight

double oomph::EBDF3::Fn_weight

private

Referenced by set_weights(), and timestep().

Yn_weight

double oomph::EBDF3::Yn_weight

private

Referenced by set_weights(), and timestep().

Ynm1_weight

double oomph::EBDF3::Ynm1_weight

private

Referenced by set_weights(), and timestep().

Ynm2_weight

double oomph::EBDF3::Ynm2_weight

private

Referenced by set_weights(), and timestep().

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

• explicit_timesteppers.h
• explicit_timesteppers.cc