Real range_ideal_len (int l, int r) const;
Real range_stiffness (int l, int r, bool stretch) const;
Real configuration_length (Real) const;
vector<Real> spring_positions () const;
Real range_ideal_len (int l, int r) const;
Real range_stiffness (int l, int r, bool stretch) const;
Real configuration_length (Real) const;
vector<Real> spring_positions () const;