ImplicitEuler.cpp

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#include "ImplicitEuler.hpp"
 
namespace polyfem::time_integrator
{
    ImplicitEuler::ImplicitEuler(const DynamicOrder dynamic_order)
        : ImplicitTimeIntegrator(dynamic_order)
    {
    }
 
    void ImplicitEuler::update_quantities(const Eigen::VectorXd &x)
    {
        const Eigen::VectorXd v = compute_velocity(x);
        set_a_prev(compute_acceleration(v));
        set_v_prev(v);
        set_x_prev(x);
    }
 
    Eigen::VectorXd ImplicitEuler::x_tilde() const
    {
        if (dynamic_order_ == DynamicOrder::First)
            return x_prev();
 
        return x_prev() + dt() * v_prev();
    }
 
    Eigen::VectorXd ImplicitEuler::compute_velocity(const Eigen::VectorXd &x) const
    {
        return (x - x_prev()) / dt();
    }
 
    Eigen::VectorXd ImplicitEuler::compute_acceleration(const Eigen::VectorXd &v) const
    {
        if (dynamic_order_ == DynamicOrder::First)
            return Eigen::VectorXd::Zero(v.size());
 
        return (v - v_prev()) / dt();
    }
 
    double ImplicitEuler::acceleration_scaling() const
    {
        if (dynamic_order_ == DynamicOrder::First)
            return dt();
 
        return dt() * dt();
    }
 
    double ImplicitEuler::dv_dx(const unsigned prev_ti) const
    {
        if (prev_ti > 1)
            return 0;
        return (prev_ti == 0 ? 1 : -1) / dt();
    }
} // namespace polyfem::time_integrator