NormalAdhesionForm.cpp

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#include "NormalAdhesionForm.hpp"
 
#include <polyfem/utils/MatrixUtils.hpp>
#include <polyfem/utils/MaybeParallelFor.hpp>
#include <polyfem/utils/Timer.hpp>
#include <polyfem/utils/Types.hpp>
 
#include <ipc/broad_phase/create_broad_phase.hpp>
#include <ipc/potentials/potential.hpp>
 
#include <algorithm>
#include <cassert>
#include <cmath>
 
namespace polyfem::solver
{
    NormalAdhesionForm::NormalAdhesionForm(const ipc::CollisionMesh &collision_mesh,
                                           const double dhat_p,
                                           const double dhat_a,
                                           const double Y,
                                           const bool is_time_dependent,
                                           const bool enable_shape_derivatives,
                                           const ipc::BroadPhaseMethod broad_phase_method,
                                           const double ccd_tolerance,
                                           const int ccd_max_iterations)
        : collision_mesh_(collision_mesh),
          dhat_p_(dhat_p),
          dhat_a_(dhat_a),
          Y_(Y),
          is_time_dependent_(is_time_dependent),
          enable_shape_derivatives_(enable_shape_derivatives),
          broad_phase_method_(broad_phase_method),
          broad_phase_(ipc::create_broad_phase(broad_phase_method)),
          tight_inclusion_ccd_(ccd_tolerance, ccd_max_iterations),
          normal_adhesion_potential_(dhat_p, dhat_a, Y, 1)
    {
        assert(dhat_p > 0);
        assert(dhat_a > dhat_p);
        assert(ccd_tolerance > 0);
 
        prev_distance_ = -1;
        collision_set_.set_enable_shape_derivatives(enable_shape_derivatives);
    }
 
    void NormalAdhesionForm::init(const Eigen::VectorXd &x)
    {
        update_collision_set(compute_displaced_surface(x));
    }
 
    void NormalAdhesionForm::update_quantities(const double t, const Eigen::VectorXd &x)
    {
        update_collision_set(compute_displaced_surface(x));
    }
 
    Eigen::MatrixXd NormalAdhesionForm::compute_displaced_surface(const Eigen::VectorXd &x) const
    {
        return collision_mesh_.displace_vertices(utils::unflatten(x, collision_mesh_.dim()));
    }
 
    void NormalAdhesionForm::update_collision_set(const Eigen::MatrixXd &displaced_surface)
    {
        // Store the previous value used to compute the constraint set to avoid duplicate computation.
        static Eigen::MatrixXd cached_displaced_surface;
        if (cached_displaced_surface.size() == displaced_surface.size() && cached_displaced_surface == displaced_surface)
            return;
 
        if (use_cached_candidates_)
            collision_set_.build(
                candidates_, collision_mesh_, displaced_surface, dhat_a_);
        else
            collision_set_.build(
                collision_mesh_, displaced_surface, dhat_a_, dmin_, broad_phase_);
        cached_displaced_surface = displaced_surface;
    }
 
    double NormalAdhesionForm::value_unweighted(const Eigen::VectorXd &x) const
    {
        return normal_adhesion_potential_(collision_set_, collision_mesh_, compute_displaced_surface(x));
    }
 
    Eigen::VectorXd NormalAdhesionForm::value_per_element_unweighted(const Eigen::VectorXd &x) const
    {
        const Eigen::MatrixXd V = compute_displaced_surface(x);
        assert(V.rows() == collision_mesh_.num_vertices());
 
        const size_t num_vertices = collision_mesh_.num_vertices();
 
        if (collision_set_.empty())
        {
            return Eigen::VectorXd::Zero(collision_mesh_.full_num_vertices());
        }
 
        const Eigen::MatrixXi &E = collision_mesh_.edges();
        const Eigen::MatrixXi &F = collision_mesh_.faces();
 
        auto storage = utils::create_thread_storage<Eigen::VectorXd>(Eigen::VectorXd::Zero(num_vertices));
 
        utils::maybe_parallel_for(collision_set_.size(), [&](int start, int end, int thread_id) {
            Eigen::VectorXd &local_storage = utils::get_local_thread_storage(storage, thread_id);
 
            for (size_t i = start; i < end; i++)
            {
                // Quadrature weight is premultiplied by compute_potential
                const double potential = normal_adhesion_potential_(collision_set_[i], collision_set_[i].dof(V, E, F));
 
                const int n_v = collision_set_[i].num_vertices();
                const auto vis = collision_set_[i].vertex_ids(E, F);
                for (int j = 0; j < n_v; j++)
                {
                    assert(0 <= vis[j] && vis[j] < num_vertices);
                    local_storage[vis[j]] += potential / n_v;
                }
            }
        });
 
        Eigen::VectorXd out = Eigen::VectorXd::Zero(num_vertices);
        for (const auto &local_potential : storage)
        {
            out += local_potential;
        }
 
        Eigen::VectorXd out_full = Eigen::VectorXd::Zero(collision_mesh_.full_num_vertices());
        for (int i = 0; i < out.size(); i++)
            out_full[collision_mesh_.to_full_vertex_id(i)] = out[i];
 
        assert(std::abs(value_unweighted(x) - out_full.sum()) < std::max(1e-10 * out_full.sum(), 1e-10));
 
        return out_full;
    }
 
    void NormalAdhesionForm::first_derivative_unweighted(const Eigen::VectorXd &x, Eigen::VectorXd &gradv) const
    {
        gradv = normal_adhesion_potential_.gradient(collision_set_, collision_mesh_, compute_displaced_surface(x));
        gradv = collision_mesh_.to_full_dof(gradv);
    }
 
    void NormalAdhesionForm::second_derivative_unweighted(const Eigen::VectorXd &x, StiffnessMatrix &hessian) const
    {
        POLYFEM_SCOPED_TIMER("normal adhesion hessian");
 
        ipc::PSDProjectionMethod psd_projection_method;
 
        if (project_to_psd_)
        {
            psd_projection_method = ipc::PSDProjectionMethod::CLAMP;
        }
        else
        {
            psd_projection_method = ipc::PSDProjectionMethod::NONE;
        }
 
        hessian = normal_adhesion_potential_.hessian(collision_set_, collision_mesh_, compute_displaced_surface(x), psd_projection_method);
        hessian = collision_mesh_.to_full_dof(hessian);
    }
 
    void NormalAdhesionForm::solution_changed(const Eigen::VectorXd &new_x)
    {
        update_collision_set(compute_displaced_surface(new_x));
    }
 
    void NormalAdhesionForm::line_search_begin(const Eigen::VectorXd &x0, const Eigen::VectorXd &x1)
    {
        candidates_.build(
            collision_mesh_,
            compute_displaced_surface(x0),
            compute_displaced_surface(x1),
            /*inflation_radius=*/dhat_a_ / 2,
            broad_phase_);
 
        use_cached_candidates_ = true;
    }
 
    void NormalAdhesionForm::line_search_end()
    {
        candidates_.clear();
        use_cached_candidates_ = false;
    }
 
    void NormalAdhesionForm::post_step(const polysolve::nonlinear::PostStepData &data)
    {
        if (data.iter_num == 0)
            return;
 
        const Eigen::MatrixXd displaced_surface = compute_displaced_surface(data.x);
 
        const double curr_distance = collision_set_.compute_minimum_distance(collision_mesh_, displaced_surface);
 
        prev_distance_ = curr_distance;
    }
 
} // namespace polyfem::solver