LStableDirk4.h

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//* This file is part of the MOOSE framework
//* https://mooseframework.inl.gov
//*
//* All rights reserved, see COPYRIGHT for full restrictions
//* https://github.com/idaholab/moose/blob/master/COPYRIGHT
//*
//* Licensed under LGPL 2.1, please see LICENSE for details
//* https://www.gnu.org/licenses/lgpl-2.1.html

#pragma once

#include "TimeIntegrator.h"

class LStableDirk4 : public TimeIntegrator
{
public:
  static InputParameters validParams();

  LStableDirk4(const InputParameters & parameters);

  virtual int order() override { return 4; }
  virtual void computeTimeDerivatives() override;
  virtual void computeADTimeDerivatives(ADReal & ad_u_dot,
                                        const dof_id_type & dof,
                                        ADReal & ad_u_dotdot) const override;
  virtual void solve() override;
  virtual void postResidual(NumericVector<Number> & residual) override;
  virtual bool overridesSolve() const override { return true; }

protected:
  template <typename T, typename T2>
  void computeTimeDerivativeHelper(T & u_dot, const T2 & u_old) const;

  // Indicates the current stage.
  unsigned int _stage;

  // The number of stages in the method.  According to S9.4.2/4 of the
  // standard, we can specify a constant initializer like this for
  // integral types, it does not have to appear outside the class
  // definition.
  static const unsigned int _n_stages = 5;

  // Store pointers to the various stage residuals
  NumericVector<Number> * _stage_residuals[_n_stages];

  // Butcher tableau "C" parameters derived from _gamma
  static const Real _c[_n_stages];

  // Butcher tableau "A" values derived from _gamma.  We only use the
  // lower triangle of this.
  static const Real _a[_n_stages][_n_stages];
};

template <typename T, typename T2>
void
LStableDirk4::computeTimeDerivativeHelper(T & u_dot, const T2 & u_old) const
{
  u_dot -= u_old;
  u_dot *= 1. / _dt;
}