AMIPSEnergy.hpp

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#pragma once
 
#include <polyfem/assembler/GenericElastic.hpp>
#include <polyfem/assembler/MatParams.hpp>
#include <polyfem/utils/Types.hpp>
#include <polyfem/utils/MatrixUtils.hpp>
 
#include <polyfem/Common.hpp>
 
#include <Eigen/Dense>
 
#include <functional>
#include <iostream>
#include <vector>
 
namespace polyfem::assembler
{
    class AMIPSEnergy : public GenericElastic<AMIPSEnergy>
    {
    public:
        AMIPSEnergy();
 
        // sets material params
        void add_multimaterial(const int index, const json &params, const Units &units) override;
 
        std::string name() const override { return "AMIPS"; }
        std::map<std::string, ParamFunc> parameters() const override;
 
        template <typename T>
        T elastic_energy(
            const RowVectorNd &p,
            const double t,
            const int el_id,
            const DefGradMatrix<T> &def_grad) const
        {
            using std::pow;
            using MatrixNT = Eigen::Matrix<T, Eigen::Dynamic, Eigen::Dynamic, 0, 3, 3>;
 
            MatrixNT F = MatrixNT::Zero(size(), size());
            for (int i = 0; i < size(); ++i)
            {
                for (int j = 0; j < size(); ++j)
                {
                    for (int k = 0; k < size(); ++k)
                    {
                        F(i, j) += def_grad(i, k) * canonical_transformation_[el_id](k, j);
                    }
                }
            }
 
            const T J = polyfem::utils::determinant(F);
            return (F.transpose() * F).trace() / pow(J, 2. / size());
        }
 
    private:
        std::vector<Eigen::MatrixXd> canonical_transformation_;
    };
} // namespace polyfem::assembler