// ******************************************************************************
   //
   // 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,
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  // ******************************************************************************
  package ffx.potential.nonbonded;
  
  import ffx.potential.MolecularAssembly;
  import ffx.potential.bonded.Atom;
  import ffx.potential.bonded.LambdaInterface;
  import ffx.potential.bonded.MSNode;
  import ffx.potential.bonded.Polymer;
  import ffx.potential.parameters.ForceField;
  
  import java.util.List;
  import java.util.logging.Logger;
  
  import static ffx.numerics.math.DoubleMath.length2;
  import static java.util.Arrays.fill;
  import static org.apache.commons.math3.util.FastMath.pow;
  
  /**
   * Restrain molecules to their center of mass.
   *
   * @author Julia Park
   * @since 1.0
   */
  public class COMRestraint implements LambdaInterface {
  
    private static final Logger logger = Logger.getLogger(COMRestraint.class.getName());
    private final Atom[] atoms;
    private final int nAtoms;
    private final Polymer[] polymers;
    private final List<MSNode> molecules;
    private final List<MSNode> water;
    private final List<MSNode> ions;
    private final int nMolecules;
    /**
     * Force constant in Kcal/mole/Angstrom.
     */
    private final double forceConstant;
  
    private final double[][] initialCOM;
    private final double[][] currentCOM;
    private final double[] dx = new double[3];
    private final double[] dcomdx;
    private final double lambdaExp = 1.0;
    private final double[] lambdaGradient;
    private double lambda = 1.0;
    private double lambdaPow = pow(lambda, lambdaExp);
    private double dLambdaPow = lambdaExp * pow(lambda, lambdaExp - 1.0);
    private double d2LambdaPow = 0;
    private double dEdL = 0.0;
    private double d2EdL2 = 0.0;
    private boolean lambdaTerm;
  
    /**
     * This COMRestraint is based on the unit cell parameters and symmetry operators of the supplied
     * crystal.
     *
     * @param molecularAssembly The MolecularAssembly to operate on.
     */
    public COMRestraint(MolecularAssembly molecularAssembly) {
      this.atoms = molecularAssembly.getAtomArray();
      nAtoms = atoms.length;
      this.polymers = molecularAssembly.getChains();
      this.molecules = molecularAssembly.getMolecules();
     this.water = molecularAssembly.getWater();
     this.ions = molecularAssembly.getIons();
     ForceField forceField = molecularAssembly.getForceField();
 
     nMolecules = countMolecules();
     initialCOM = new double[3][nMolecules];
     currentCOM = new double[3][nMolecules];
 
     // lambdaTerm = forceField.getBoolean("LAMBDATERM", false);
     lambdaTerm = false;
 
     if (lambdaTerm) {
       lambdaGradient = new double[nAtoms * 3];
     } else {
       lambdaGradient = null;
       lambda = 1.0;
       lambdaPow = 1.0;
       dLambdaPow = 0.0;
       d2LambdaPow = 0.0;
     }
     dcomdx = new double[nAtoms];
     forceConstant = forceField.getDouble("COMRESTRAINT_K", 10.0);
 
     computeCOM(initialCOM, nMolecules);
 
     logger.info("\n COM restraint initialized");
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public double getLambda() {
     return lambda;
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public void setLambda(double lambda) {
     if (lambdaTerm) {
       this.lambda = lambda;
 
       double lambdaWindow = 1.0;
 
       if (this.lambda <= lambdaWindow) {
         double dldgl = 1.0 / lambdaWindow;
         double l = dldgl * this.lambda;
         double l2 = l * l;
         double l3 = l2 * l;
         double l4 = l2 * l2;
         double l5 = l4 * l;
         double c3 = 10.0;
         double c4 = -15.0;
         double c5 = 6.0;
         double threeC3 = 3.0 * c3;
         double sixC3 = 6.0 * c3;
         double fourC4 = 4.0 * c4;
         double twelveC4 = 12.0 * c4;
         double fiveC5 = 5.0 * c5;
         double twentyC5 = 20.0 * c5;
         lambdaPow = c3 * l3 + c4 * l4 + c5 * l5;
         dLambdaPow = (threeC3 * l2 + fourC4 * l3 + fiveC5 * l4) * dldgl;
         d2LambdaPow = (sixC3 * l + twelveC4 * l2 + twentyC5 * l3) * dldgl * dldgl;
       } else {
         lambdaPow = 1.0;
         dLambdaPow = 0.0;
         d2LambdaPow = 0.0;
       }
     } else {
       this.lambda = 1.0;
       lambdaPow = 1.0;
       dLambdaPow = 0.0;
       d2LambdaPow = 0.0;
     }
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public double getd2EdL2() {
     if (lambdaTerm) {
       return d2EdL2;
     } else {
       return 0.0;
     }
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public double getdEdL() {
     if (lambdaTerm) {
       return dEdL;
     } else {
       return 0.0;
     }
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public void getdEdXdL(double[] gradient) {
     if (lambdaTerm) {
       int n3 = nAtoms * 3;
       for (int i = 0; i < n3; i++) {
         gradient[i] += lambdaGradient[i];
       }
     }
   }
 
   /**
    * residual.
    *
    * @param gradient a boolean.
    * @param print    a boolean.
    * @return a double.
    */
   public double residual(boolean gradient, boolean print) {
     if (lambdaTerm) {
       dEdL = 0.0;
       d2EdL2 = 0.0;
       fill(lambdaGradient, 0.0);
     }
     double residual = 0.0;
     double fx2 = forceConstant * 2.0;
     computeCOM(currentCOM, nMolecules);
     computedcomdx();
     for (int i = 0; i < nMolecules; i++) {
       dx[0] = currentCOM[0][i] - initialCOM[0][i];
       dx[1] = currentCOM[1][i] - initialCOM[1][i];
       dx[2] = currentCOM[2][i] - initialCOM[2][i];
 
       double r2 = length2(dx);
       residual += r2;
       for (int j = 0; j < nAtoms; j++) {
         if (gradient || lambdaTerm) {
           final double dedx = dx[0] * fx2 * dcomdx[j];
           final double dedy = dx[1] * fx2 * dcomdx[j];
           final double dedz = dx[2] * fx2 * dcomdx[j];
           // Current atomic coordinates.
           Atom atom = atoms[j];
           if (gradient) {
             atom.addToXYZGradient(lambdaPow * dedx, lambdaPow * dedy, lambdaPow * dedz);
           }
           if (lambdaTerm) {
             int j3 = i * 3;
             lambdaGradient[j3] = dLambdaPow * dedx;
             lambdaGradient[j3 + 1] = dLambdaPow * dedy;
             lambdaGradient[j3 + 2] = dLambdaPow * dedz;
           }
         }
       }
     }
     if (lambdaTerm) {
       dEdL = dLambdaPow * forceConstant * residual;
       d2EdL2 = d2LambdaPow * forceConstant * residual;
     }
     return forceConstant * residual * lambdaPow;
   }
 
   /**
    * Setter for the field <code>lambdaTerm</code>.
    *
    * @param lambdaTerm a boolean.
    */
   public void setLambdaTerm(boolean lambdaTerm) {
     this.lambdaTerm = lambdaTerm;
     setLambda(lambda);
   }
 
   private void computeCOM(double[][] com, int nMolecules) {
     int i = 0;
     while (i < nMolecules) {
       if (polymers != null && polymers.length > 0) {
         // Find the center of mass
         for (Polymer polymer : polymers) {
           List<Atom> list = polymer.getAtomList();
           com[0][i] = 0.0;
           com[1][i] = 0.0;
           com[2][i] = 0.0;
           double totalMass = 0.0;
           for (Atom atom : list) {
             double m = atom.getMass();
             com[0][i] += atom.getX() * m;
             com[1][i] += atom.getY() * m;
             com[2][i] += atom.getZ() * m;
             totalMass += m;
           }
           com[0][i] /= totalMass;
           com[1][i] /= totalMass;
           com[2][i] /= totalMass;
           i++;
         }
       }
 
       // Loop over each molecule
       for (MSNode molecule : molecules) {
         List<Atom> list = molecule.getAtomList();
         // Find the center of mass
         com[0][i] = 0.0;
         com[1][i] = 0.0;
         com[2][i] = 0.0;
         double totalMass = 0.0;
         for (Atom atom : list) {
           double m = atom.getMass();
           com[0][i] += atom.getX() * m;
           com[1][i] += atom.getY() * m;
           com[2][i] += atom.getZ() * m;
           totalMass += m;
         }
         com[0][i] /= totalMass;
         com[1][i] /= totalMass;
         com[2][i] /= totalMass;
         i++;
       }
 
       // Loop over each water
       for (MSNode water : water) {
         List<Atom> list = water.getAtomList();
         // Find the center of mass
         com[0][i] = 0.0;
         com[1][i] = 0.0;
         com[2][i] = 0.0;
         double totalMass = 0.0;
         for (Atom atom : list) {
           double m = atom.getMass();
           com[0][i] += atom.getX() * m;
           com[1][i] += atom.getY() * m;
           com[2][i] += atom.getZ() * m;
           totalMass += m;
         }
         com[0][i] /= totalMass;
         com[1][i] /= totalMass;
         com[2][i] /= totalMass;
         i++;
       }
 
       // Loop over each ion
       for (MSNode ion : ions) {
         List<Atom> list = ion.getAtomList();
         // Find the center of mass
         com[0][i] = 0.0;
         com[1][i] = 0.0;
         com[2][i] = 0.0;
         double totalMass = 0.0;
         for (Atom atom : list) {
           double m = atom.getMass();
           com[0][i] += atom.getX() * m;
           com[1][i] += atom.getY() * m;
           com[2][i] += atom.getZ() * m;
           totalMass += m;
         }
         com[0][i] /= totalMass;
         com[1][i] /= totalMass;
         com[2][i] /= totalMass;
         i++;
       }
     }
   }
 
   private void computedcomdx() {
     //        double totalMass = 0.0;
     int i = 0;
     while (i < nAtoms) {
       if (polymers != null && polymers.length > 0) {
         for (Polymer polymer : polymers) {
           List<Atom> list = polymer.getAtomList();
           double totalMass = 0.0;
           for (Atom atom : list) {
             double m = atom.getMass();
             totalMass += m;
           }
           for (Atom atom : list) {
             dcomdx[i] = atom.getMass();
             dcomdx[i] /= totalMass;
             i++;
           }
         }
       }
 
       // Loop over each molecule
       for (MSNode molecule : molecules) {
         List<Atom> list = molecule.getAtomList();
         double totalMass = 0.0;
         for (Atom atom : list) {
           double m = atom.getMass();
           totalMass += m;
         }
         for (Atom atom : list) {
           dcomdx[i] = atom.getMass();
           dcomdx[i] /= totalMass;
           i++;
         }
       }
 
       // Loop over each water
       for (MSNode water : water) {
         List<Atom> list = water.getAtomList();
         double totalMass = 0.0;
         for (Atom atom : list) {
           double m = atom.getMass();
           totalMass += m;
         }
         for (Atom atom : list) {
           dcomdx[i] = atom.getMass();
           dcomdx[i] /= totalMass;
           i++;
         }
       }
 
       // Loop over each ion
       for (MSNode ion : ions) {
         List<Atom> list = ion.getAtomList();
         double totalMass = 0.0;
         for (Atom atom : list) {
           double m = atom.getMass();
           totalMass += m;
         }
         for (Atom atom : list) {
           dcomdx[i] = atom.getMass();
           dcomdx[i] /= totalMass;
           i++;
         }
       }
     }
     //        for (int i = 0; i < nAtoms; i++) {
     //            Atom a = atoms[i];
     //            dcomdx[j] = a.getMass() / totalMass;
     //        }
 
   }
 
   private int countMolecules() {
     int count = 0;
     // Move polymers togethers.
     if (polymers != null && polymers.length > 0) {
       count += polymers.length;
     }
     if (molecules != null) {
       count += molecules.size();
     }
     if (water != null) {
       count += water.size();
     }
     if (ions != null) {
       count += ions.size();
     }
     return count;
   }
 }