WR2ExplicitExponentialTimeIntegration.cxx

// Copyright 2023, UChicago Argonne, LLC
// All Rights Reserved
// Software Name: NEML2 -- the New Engineering material Model Library, version 2
// By: Argonne National Laboratory
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#include "neml2/models/WR2ExplicitExponentialTimeIntegration.h"
#include "neml2/tensors/tensors.h"
 
namespace neml2
{
register_NEML2_object(WR2ExplicitExponentialTimeIntegration);
 
OptionSet
WR2ExplicitExponentialTimeIntegration::expected_options()
{
  OptionSet options = Model::expected_options();
  options.doc() = "Perform explicit discrete exponential time integration of a rotation. The "
                  "update can be written as \\f$ s = \\exp\\left[ (t-t_n)\\dot{s}\\right] \\circ "
                  "s_n \\f$, where \\f$ \\circ \\f$ denotes the rotation operator.";
 
  options.set<VariableName>("variable");
  options.set("variable").doc() = "Variable being integrated";
 
  options.set<VariableName>("time") = VariableName("t");
  options.set("time").doc() = "Time";
 
  return options;
}
 
WR2ExplicitExponentialTimeIntegration::WR2ExplicitExponentialTimeIntegration(
    const OptionSet & options)
  : Model(options),
    _var_name(options.get<VariableName>("variable")),
    _var_rate_name(_var_name.with_suffix("_rate")),
    _s(declare_output_variable<Rot>(_var_name.on("state"))),
    _s_dot(declare_input_variable<WR2>(_var_rate_name.on("state"))),
    _sn(declare_input_variable<Rot>(_var_name.on("old_state"))),
    _t(declare_input_variable<Scalar>(options.get<VariableName>("time").on("forces"))),
    _tn(declare_input_variable<Scalar>(options.get<VariableName>("time").on("old_forces")))
{
}
 
void
WR2ExplicitExponentialTimeIntegration::set_value(bool out, bool dout_din, bool d2out_din2)
{
  neml_assert_dbg(!d2out_din2, "Second derivative not implemented.");
 
  const auto dt = _t - _tn;
 
  // Incremental rotation
  const auto inc = (_s_dot * dt).exp();
 
  if (out)
    _s = Rot(_sn).rotate(inc);
 
  if (dout_din)
  {
    const auto de = (_s_dot * dt).dexp();
    _s.d(_s_dot) = Rot(_sn).drotate(inc) * de * dt;
    if (Model::stage == Model::Stage::UPDATING)
    {
      _s.d(_sn) = Rot(_sn).drotate_self(inc);
      _s.d(_t) = Rot(_sn).drotate(inc) * de * Vec(_s_dot.value());
      _s.d(_tn) = -Rot(_sn).drotate(inc) * de * Vec(_s_dot.value());
    }
  }
}
 
} // namespace neml2