// ******************************************************************************
   //
   // Title:       Force Field X.
   // Description: Force Field X - Software for Molecular Biophysics.
   // Copyright:   Copyright (c) Michael J. Schnieders 2001-2025.
   //
   // This file is part of Force Field X.
   //
   // Force Field X is free software; you can redistribute it and/or modify it
  // under the terms of the GNU General Public License version 3 as published by
  // the Free Software Foundation.
  //
  // Force Field X is distributed in the hope that it will be useful, but WITHOUT
  // ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
  // FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
  // details.
  //
  // You should have received a copy of the GNU General Public License along with
  // Force Field X; if not, write to the Free Software Foundation, Inc., 59 Temple
  // Place, Suite 330, Boston, MA 02111-1307 USA
  //
  // Linking this library statically or dynamically with other modules is making a
  // combined work based on this library. Thus, the terms and conditions of the
  // GNU General Public License cover the whole combination.
  //
  // As a special exception, the copyright holders of this library give you
  // permission to link this library with independent modules to produce an
  // executable, regardless of the license terms of these independent modules, and
  // to copy and distribute the resulting executable under terms of your choice,
  // provided that you also meet, for each linked independent module, the terms
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  // module which is not derived from or based on this library. If you modify this
  // library, you may extend this exception to your version of the library, but
  // you are not obligated to do so. If you do not wish to do so, delete this
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  // ******************************************************************************
  package ffx.openmm;
  
  import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableLangevinIntegrator_create;
  import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableLangevinIntegrator_destroy;
  import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableLangevinIntegrator_getErrorTolerance;
  import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableLangevinIntegrator_getFriction;
  import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableLangevinIntegrator_getMaximumStepSize;
  import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableLangevinIntegrator_getRandomNumberSeed;
  import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableLangevinIntegrator_getTemperature;
  import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableLangevinIntegrator_setErrorTolerance;
  import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableLangevinIntegrator_setFriction;
  import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableLangevinIntegrator_setMaximumStepSize;
  import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableLangevinIntegrator_setRandomNumberSeed;
  import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableLangevinIntegrator_setTemperature;
  import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableLangevinIntegrator_step;
  import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableLangevinIntegrator_stepTo;
  
  /**
   * This class implements a Langevin integrator with variable time stepping.
   * The integrator automatically adjusts the step size to maintain a specified
   * error tolerance, making it suitable for systems with widely varying time scales.
   * <p>
   * The variable step size algorithm monitors the local truncation error and
   * adjusts the step size accordingly. This can lead to more efficient integration
   * for systems where different parts evolve on different time scales, such as
   * systems with both fast vibrations and slow conformational changes.
   */
  public class VariableLangevinIntegrator extends Integrator {
  
    /**
     * Create a VariableLangevinIntegrator.
     *
     * @param temperature   The temperature of the heat bath (in Kelvin).
     * @param frictionCoeff The friction coefficient which couples the system to the heat bath (in 1/ps).
     * @param errorTol      The error tolerance for adaptive step sizing.
     */
    public VariableLangevinIntegrator(double temperature, double frictionCoeff, double errorTol) {
      super(OpenMM_VariableLangevinIntegrator_create(temperature, frictionCoeff, errorTol));
    }
  
    /**
     * Destroy the integrator.
     */
    @Override
    public void destroy() {
      if (pointer != null) {
        OpenMM_VariableLangevinIntegrator_destroy(pointer);
        pointer = null;
      }
    }
  
    /**
     * Get the error tolerance for adaptive step sizing.
     *
     * @return The error tolerance.
     */
    public double getErrorTolerance() {
      return OpenMM_VariableLangevinIntegrator_getErrorTolerance(pointer);
    }
  
    /**
     * Get the friction coefficient which determines how strongly the system is coupled to
    * the heat bath (in 1/ps).
    *
    * @return The friction coefficient.
    */
   public double getFriction() {
     return OpenMM_VariableLangevinIntegrator_getFriction(pointer);
   }
 
   /**
    * Get the maximum step size the integrator is allowed to use (in ps).
    *
    * @return The maximum step size.
    */
   public double getMaximumStepSize() {
     return OpenMM_VariableLangevinIntegrator_getMaximumStepSize(pointer);
   }
 
   /**
    * Get the random number seed. See setRandomNumberSeed() for details.
    *
    * @return The random number seed.
    */
   public int getRandomNumberSeed() {
     return OpenMM_VariableLangevinIntegrator_getRandomNumberSeed(pointer);
   }
 
   /**
    * Get the temperature of the heat bath (in Kelvin).
    *
    * @return The temperature of the heat bath.
    */
   public double getTemperature() {
     return OpenMM_VariableLangevinIntegrator_getTemperature(pointer);
   }
 
   /**
    * Set the error tolerance for adaptive step sizing.
    *
    * @param tol The error tolerance.
    */
   public void setErrorTolerance(double tol) {
     OpenMM_VariableLangevinIntegrator_setErrorTolerance(pointer, tol);
   }
 
   /**
    * Set the friction coefficient which determines how strongly the system is coupled to
    * the heat bath (in 1/ps).
    *
    * @param coeff The friction coefficient.
    */
   public void setFriction(double coeff) {
     OpenMM_VariableLangevinIntegrator_setFriction(pointer, coeff);
   }
 
   /**
    * Set the maximum step size the integrator is allowed to use (in ps).
    *
    * @param size The maximum step size.
    */
   public void setMaximumStepSize(double size) {
     OpenMM_VariableLangevinIntegrator_setMaximumStepSize(pointer, size);
   }
 
   /**
    * Set the random number seed. The precise meaning of this parameter is undefined, and is left up
    * to each Platform to interpret in an appropriate way. It is guaranteed that if two simulations
    * are run with different random number seeds, the sequence of random numbers will be different.
    * On the other hand, no guarantees are made about the behavior of simulations that use the same seed.
    * In particular, Platforms are permitted to use non-deterministic algorithms which produce different
    * results on successive runs, even if those runs were initialized identically.
    * <p>
    * If seed is set to 0 (which is the default value assigned), a unique seed is chosen when a Context
    * is created from this Force. This is done to ensure that each Context receives unique random seeds
    * without you needing to set them explicitly.
    *
    * @param seed The random number seed.
    */
   public void setRandomNumberSeed(int seed) {
     OpenMM_VariableLangevinIntegrator_setRandomNumberSeed(pointer, seed);
   }
 
   /**
    * Set the temperature of the heat bath (in Kelvin).
    *
    * @param temp The temperature of the heat bath.
    */
   public void setTemperature(double temp) {
     OpenMM_VariableLangevinIntegrator_setTemperature(pointer, temp);
   }
 
   /**
    * Advance a simulation through time by taking a series of time steps.
    *
    * @param steps The number of time steps to take.
    */
   public void step(int steps) {
     OpenMM_VariableLangevinIntegrator_step(pointer, steps);
   }
 
   /**
    * Advance the simulation by integrating until a specified time is reached.
    *
    * @param time The time to which the simulation should be advanced (in ps).
    */
   public void stepTo(double time) {
     OpenMM_VariableLangevinIntegrator_stepTo(pointer, time);
   }
 }