chomp_cost.cpp

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/* Author: Mrinal Kalakrishnan */

#include <chomp_motion_planner/chomp_cost.h>
#include <chomp_motion_planner/chomp_utils.h>
#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()
{
}

}