Force

// ******************************************************************************
//
// 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.
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// 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
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// ******************************************************************************
package ffx.openmm;

import com.sun.jna.Pointer;
import com.sun.jna.ptr.PointerByReference;

import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_Boolean.OpenMM_True;
import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_Force_getForceGroup;
import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_Force_getName;
import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_Force_setForceGroup;
import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_Force_setName;
import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_Force_usesPeriodicBoundaryConditions;

/**
 * Force objects apply forces to the particles in a System, or alter their behavior in other
 * ways. This is an abstract class. Subclasses define particular forces.
 * <p>
 * More specifically, a Force object can do any or all of the following:
 *
 * <ul>
 * <li>Add a contribution to the force on each particle</li>
 * <li>Add a contribution to the potential energy of the System</li>
 * <li>Modify the positions and velocities of particles at the start of each time step</li>
 * <li>Define parameters which are stored in the Context and can be modified by the user</li>
 * <li>Change the values of parameters defined by other Force objects at the start of each time step</li>
 * </ul>
 * <p>
 * Forces may be organized into "force groups". This is used for multiple time step integration,
 * and allows subsets of the Forces in a System to be evaluated at different times. By default,
 * all Forces are in group 0. Call setForceGroup() to change this. Some Force subclasses may
 * provide additional methods to further split their computations into multiple groups.  Be aware
 * that particular Platforms may place restrictions on the use of force groups, such as requiring
 * all nonbonded forces to be in the same group.
 */
public abstract class Force {

  /**
   * The forcePointer is allocated and deallocated by classes that extend OpenMMForce.
   */
  protected PointerByReference pointer = null;

  /**
   * The forceIndex is returned by OpenMMSystem.addForce and is used to remove the force.
   */
  private int forceIndex = -1;

  /**
   * Create a new Force object with the specified pointer.
   *
   * @param pointer A pointer to the native OpenMM Force object.
   */
  public Force(PointerByReference pointer) {
    if (pointer == null || pointer.getValue() == null) {
      throw new IllegalArgumentException("Pointer cannot be null.");
    }
    this.pointer = pointer;
  }

  /**
   * Destroy the force.
   */
  public abstract void destroy();

  /**
   * Get the pointer to the OpenMM Force.
   *
   * @return The pointer to the OpenMM Force.
   */
  public PointerByReference getPointer() {
    return pointer;
  }

  /**
   * Set the force group.
   *
   * @param forceGroup The force group.
   */
  public void setForceGroup(int forceGroup) {
    OpenMM_Force_setForceGroup(pointer, forceGroup);
  }

  /**
   * Get the force group.
   *
   * @return The force group.
   */
  public int getForceGroup() {
    return OpenMM_Force_getForceGroup(pointer);
  }

  /**
   * Set the name of the force.
   *
   * @param name The name of the force.
   */
  public void setName(String name) {
    OpenMM_Force_setName(pointer, name);
  }

  /**
   * Get the name of the force.
   *
   * @return The name of the force.
   */
  public String getName() {
    Pointer pointer = OpenMM_Force_getName(this.pointer);
    if (pointer == null) {
      return null;
    }
    return pointer.getString(0);
  }

  /**
   * Set the force index.
   *
   * @param forceIndex The force index.
   */
  public void setForceIndex(int forceIndex) {
    this.forceIndex = forceIndex;
  }

  /**
   * Get the force index.
   *
   * @return The force index.
   */
  public int getForceIndex() {
    return forceIndex;
  }

  /**
   * Check if the force use periodic boundary conditions. This is a virtual method
   * that must be implemented by classes that extend OpenMMForce.
   *
   * @return True if the force uses periodic boundary conditions.
   */
  public boolean usesPeriodicBoundaryConditions() {
    int pbc = OpenMM_Force_usesPeriodicBoundaryConditions(pointer);
    return pbc == OpenMM_True;
  }

}