LStableDirk2.h

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//* This file is part of the MOOSE framework
//* https://www.mooseframework.org
//*
//* 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 LStableDirk2 : public TimeIntegrator
{
public:
  static InputParameters validParams();

  LStableDirk2(const InputParameters & parameters);

  virtual int order() override { return 2; }
  virtual void computeTimeDerivatives() override;
  void computeADTimeDerivatives(DualReal & ad_u_dot,
                                const dof_id_type & dof,
                                DualReal & ad_u_dotdot) const override;
  virtual void solve() override;
  virtual void postResidual(NumericVector<Number> & residual) override;

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

  unsigned int _stage;

  NumericVector<Number> & _residual_stage1;

  NumericVector<Number> & _residual_stage2;

  // The parameter of the method, set at construction time and cannot be changed.
  const Real _alpha;
};

template <typename T, typename T2>
void
LStableDirk2::computeTimeDerivativeHelper(T & u_dot, const T2 & u_old) const
{
  u_dot -= u_old;
  u_dot *= 1. / _dt;
}