chomp_cost.cpp

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/* Author: Mrinal Kalakrishnan */
 
#include <chomp_motion_planner/chomp_cost.hpp>
#include <chomp_motion_planner/chomp_utils.hpp>
 
#include <eigen3/Eigen/LU>
 
using namespace Eigen;
using namespace std;
 
namespace chomp
{
ChompCost::ChompCost(const ChompTrajectory& trajectory, int /* joint_number */,
                     const std::vector<double>& derivative_costs, double ridge_factor)
{
  int num_vars_all = trajectory.getNumPoints();
  int num_vars_free = num_vars_all - 2 * (DIFF_RULE_LENGTH - 1);
  MatrixXd diff_matrix = MatrixXd::Zero(num_vars_all, num_vars_all);
  quad_cost_full_ = MatrixXd::Zero(num_vars_all, num_vars_all);
 
  // construct the quad cost for all variables, as a sum of squared differentiation matrices
  double multiplier = 1.0;
  for (unsigned int i = 0; i < derivative_costs.size(); ++i)
  {
    multiplier *= trajectory.getDiscretization();
    diff_matrix = getDiffMatrix(num_vars_all, &DIFF_RULES[i][0]);
    quad_cost_full_ += (derivative_costs[i] * multiplier) * (diff_matrix.transpose() * diff_matrix);
  }
  quad_cost_full_ += MatrixXd::Identity(num_vars_all, num_vars_all) * ridge_factor;
 
  // extract the quad cost just for the free variables:
  quad_cost_ = quad_cost_full_.block(DIFF_RULE_LENGTH - 1, DIFF_RULE_LENGTH - 1, num_vars_free, num_vars_free);
 
  // invert the matrix:
  quad_cost_inv_ = quad_cost_.inverse();
 
  // cout << quad_cost_inv_ << endl;
}
 
Eigen::MatrixXd ChompCost::getDiffMatrix(int size, const double* diff_rule) const
{
  MatrixXd matrix = MatrixXd::Zero(size, size);
  for (int i = 0; i < size; ++i)
  {
    for (int j = -DIFF_RULE_LENGTH / 2; j <= DIFF_RULE_LENGTH / 2; ++j)
    {
      int index = i + j;
      if (index < 0)
        continue;
      if (index >= size)
        continue;
      matrix(i, index) = diff_rule[j + DIFF_RULE_LENGTH / 2];
    }
  }
  return matrix;
}
 
double ChompCost::getMaxQuadCostInvValue() const
{
  return quad_cost_inv_.maxCoeff();
}
 
void ChompCost::scale(double scale)
{
  double inv_scale = 1.0 / scale;
  quad_cost_inv_ *= inv_scale;
  quad_cost_ *= scale;
  quad_cost_full_ *= scale;
}
 
ChompCost::~ChompCost() = default;
}  // namespace chomp