#ifndef RELAX_DATA_H
#define RELAX_DATA_H

#include <vector>

/**
 * @brief Unified data structure for geometry optimization algorithms.
 * 
 * This class provides a common data container for all relaxation methods
 * (BFGS, CG, SD, etc.) to share and reuse key variables like positions,
 * gradients, and move vectors. It serves as the single source of truth
 * for optimization state across different algorithms.
 */
class Relax_Data {
public:
 /**
 * @brief Default constructor.
 */
 Relax_Data() = default;

 /**
 * @brief Default destructor.
 */
 ~Relax_Data() = default;

 /**
 * @brief Allocate memory for data vectors.
 * @param dim_in Dimension of the optimization problem (3 * number of atoms).
 */
 void allocate(const int dim_in);

 // Static members - shared global state across all relaxation instances
 static int dim; ///< Dimension of free variables (3 * number of atoms) for ion movement
 static int dim_lattice; ///< Dimension of free variables (9) for lattice change

 static double largest_grad; ///< Largest gradient component (force) in current step

 // Instance members - per-iteration data
 std::vector<double> pos; ///< Current atomic positions in Bohr
 std::vector<double> grad; ///< Current gradient (negative force) in Ry/Bohr
 std::vector<double> move; ///< Displacement vector for next step

 std::vector<double> pos_p; ///< Previous atomic positions
 std::vector<double> grad_p; ///< Previous gradient
 std::vector<double> move_p; ///< Previous displacement
};

#endif