OptimizationInterface

// ******************************************************************************
//
// Title:       Force Field X.
// Description: Force Field X - Software for Molecular Biophysics.
// Copyright:   Copyright (c) Michael J. Schnieders 2001-2025.
//
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//
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package ffx.numerics;

import javax.annotation.Nullable;
import java.util.Collections;
import java.util.List;

/**
 * The OptimizationInterface defines methods required by an optimizer.
 *
 * @author Michael J. Schnieders
 * @since 1.0
 */
public interface OptimizationInterface {

  /**
   * Destroys this Potential and frees up any associated resources, particularly worker Threads.
   * Default implementation is to return true (assume destruction successful).
   *
   * @return If resource reclamation successful, or resources already reclaimed.
   */
  default boolean destroy() {
    return true;
  }

  /**
   * This method is called repeatedly to compute the function energy.
   *
   * @param x Input parameters.
   * @return Function value at <code>x</code>.
   * @since 1.0
   */
  double energy(double[] x);

  /**
   * This method is called repeatedly to compute the function energy. The verbose flag may not be
   * used by all implementations.
   *
   * @param x       Input parameters.
   * @param verbose Display extra information.
   * @return Function value at <code>x</code>
   */
  default double energy(double[] x, boolean verbose) {
    return energy(x);
  }

  /**
   * This method is called repeatedly to compute the function energy and gradient.
   *
   * @param x Input parameters.
   * @param g Output gradients with respect to each parameter.
   * @return Function value at <code>x</code>.
   * @since 1.0
   */
  double energyAndGradient(double[] x, double[] g);

  /**
   * This method is called repeatedly to compute the function energy and gradient. The verbose flag
   * may not be used by all implementations.
   *
   * @param x       Input parameters.
   * @param g       Output gradients with respect to each parameter.
   * @param verbose Display extra information.
   * @return Function value at <code>x</code>.
   * @since 1.0
   */
  default double energyAndGradient(double[] x, double[] g, boolean verbose) {
    return energyAndGradient(x, g);
  }

  /**
   * Load the current value of the parameters. If the supplied array is null or not large enough, a
   * new one should be created. The filled array is returned.
   *
   * @param parameters Supplied array.
   * @return The array filled with parameter values.
   */
  double[] getCoordinates(double[] parameters);

  /**
   * Set the current value of the parameters. If the supplied array is null or not large enough,
   * no action is taken.
   *
   * @param parameters The array with parameter values.
   */
  void setCoordinates(double[] parameters);

  /**
   * Get the number of variables being operated on.
   *
   * @return Number of variables.
   */
  int getNumberOfVariables();

  /**
   * Get the problem scaling.
   *
   * @return The scaling value used for each variable.
   * @since 1.0
   */
  double[] getScaling();

  /**
   * Scale the problem. A good choice for optimization is the square root of the median eigenvalue of
   * a typical Hessian.
   *
   * @param scaling The scaling value to use for each variable.
   * @since 1.0
   */
  void setScaling(@Nullable double[] scaling);

  /**
   * Get the total energy of the system
   *
   * @return the total energy
   */
  double getTotalEnergy();

  /**
   * Returns a List of Potentials this Potential depends on with a recursive search, excluding the
   * top level of this call. May not be implemented for all Potentials.
   *
   * @return By default, an empty list.
   */
  default List<Potential> getUnderlyingPotentials() {
    return Collections.emptyList();
  }

  /**
   * Default method to scale coordinates.
   *
   * @param x Input parameters.
   */
  default void scaleCoordinates(double[] x) {
    double[] scaling = getScaling();
    if (scaling != null) {
      int nParams = x.length;
      for (int i = 0; i < nParams; i++) {
        x[i] *= scaling[i];
      }
    }
  }

  /**
   * Default method to unscale coordinates.
   *
   * @param x Input parameters.
   * @param g Gradient array.
   */
  default void scaleCoordinatesAndGradient(double[] x, double[] g) {
    double[] scaling = getScaling();
    if (scaling != null) {
      int len = x.length;
      for (int i = 0; i < len; i++) {
        x[i] *= scaling[i];
        g[i] /= scaling[i];
      }
    }
  }

  /**
   * Default method to unscale coordinates.
   *
   * @param x Input parameters.
   */
  default void unscaleCoordinates(double[] x) {
    double[] scaling = getScaling();
    if (scaling != null) {
      int nParams = x.length;
      for (int i = 0; i < nParams; i++) {
        x[i] /= scaling[i];
      }
    }
  }
}