// ******************************************************************************
   //
   // 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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  // ******************************************************************************
  package ffx.numerics.integrate;
  
  import static ffx.numerics.integrate.FunctionDataCurve.approxEquals;
  import static java.lang.String.format;
  import static java.lang.System.arraycopy;
  
  /**
   * Describes a set of x, f(x) obtained by some mechanism; intended for numerical integration.
   *
   * @author Jacob M. Litman
   */
  public class DoublesDataSet implements DataSet {
  
    /** An array of input points. */
    private final double[] x;
    /** An array of results f(x). */
    private final double[] fX;
    /** Lower bound. */
    private final double lb;
    /** Upper bound. */
    private final double ub;
    /** Number of data points. */
    private final int nX;
    /** Bin size. */
    private final double sep;
    /** If ends should have 1/2 regular separation. */
    private final boolean halfWidthEnd;
  
    /**
     * Constructs a DataSet from actual data, with no known underlying function (or at least none with
     * an analytically solved integral). Assumes no half-width end bins (such as found in OST).
     *
     * @param x Points where f(x) is known
     * @param fX Values/estimates of f(x)
     */
    public DoublesDataSet(double[] x, double[] fX) {
      this(x, fX, false);
    }
  
    /**
     * Constructs a DataSet from actual data, with no known underlying function (or at least none with
     * an analytically solved integral).
     *
     * @param x Points where f(x) is known
     * @param fX Values/estimates of f(x)
     * @param halvedEnds Whether the first and last bins are half-width (such as OST)
     */
    public DoublesDataSet(double[] x, double[] fX, boolean halvedEnds) {
      nX = x.length;
      assert nX == fX.length;
  
      this.x = new double[nX];
      arraycopy(x, 0, this.x, 0, nX);
  
      this.fX = new double[nX];
      arraycopy(fX, 0, this.fX, 0, nX);
  
      lb = x[0];
      ub = x[nX - 1];
      // sep = ((ub - lb) / ((double) nX));
      halfWidthEnd = halvedEnds;
      double sepDist = ub - lb;
     sep = halfWidthEnd ? (sepDist / ((double) nX - 2)) : (sepDist / ((double) nX - 1));
     assertXIntegrity(this.x);
   }
 
   /**
    * Constructs a DataSet from another DataSet, effectively masquerading a test set such as a sine
    * wave as data from an "unknown" function. Used primarily for testing purposes.
    *
    * @param set DataSet to cast
    */
   public DoublesDataSet(DataSet set) {
     nX = set.numPoints();
 
     this.x = new double[nX];
     arraycopy(set.getX(), 0, this.x, 0, nX);
 
     this.fX = new double[nX];
     arraycopy(set.getAllFxPoints(), 0, this.fX, 0, nX);
 
     lb = x[0];
     ub = x[nX - 1];
     this.halfWidthEnd = set.halfWidthEnds();
     sep = set.binWidth();
     // Possibly add assertion for separation distance
     assertXIntegrity(x);
   }
 
   /** {@inheritDoc} */
   @Override
   public double binWidth() {
     return sep;
   }
 
   /** {@inheritDoc} */
   @Override
   public double[] getAllFxPoints() {
     double[] pts = new double[nX];
     arraycopy(fX, 0, pts, 0, nX);
     return pts;
   }
 
   /** {@inheritDoc} */
   @Override
   public double getFxPoint(int index) {
     return fX[index];
   }
 
   /** {@inheritDoc} */
   @Override
   public double[] getX() {
     double[] copyX = new double[x.length];
     arraycopy(x, 0, copyX, 0, x.length);
     return copyX;
   }
 
   /** {@inheritDoc} */
   @Override
   public boolean halfWidthEnds() {
     return halfWidthEnd;
   }
 
   /** {@inheritDoc} */
   @Override
   public double lowerBound() {
     return lb;
   }
 
   /** {@inheritDoc} */
   @Override
   public int numPoints() {
     return x.length;
   }
 
   /** {@inheritDoc} */
   @Override
   public String toString() {
     StringBuilder sb =
         new StringBuilder(
             format(
                 "Data set with %d points from lower bound %9.3g and upper bound %9.3g",
                 nX, lb, ub));
     if (halfWidthEnd) {
       sb.append(" and half-width start/end bins");
     }
     sb.append(".");
     return sb.toString();
   }
 
   /** {@inheritDoc} */
   @Override
   public double upperBound() {
     return ub;
   }
 
   /**
    * Used to check that the passed-in x array is composed of equally-spaced points from lb to ub.
    *
    * @param x The array to check.
    */
   private void assertXIntegrity(double[] x) {
     assert ub > lb;
     if (halfWidthEnd) {
       assert x.length == nX;
       assert lb == x[0];
       assert ub == x[nX - 1];
 
       assert approxEquals(x[1], lb + 0.5 * sep);
       assert approxEquals(x[nX - 2], (ub - 0.5 * sep));
 
       for (int i = 2; i < (nX - 2); i++) {
         double target = lb + 0.5 * sep;
         target += ((i - 1) * sep);
         assert approxEquals(x[i], target);
       }
     } else {
       for (int i = 0; i < x.length; i++) {
         assert approxEquals(x[i], x[0] + i * sep);
       }
     }
   }
 }