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/*
 * Carrot2 project.
 *
 * Copyright (C) 2002-2021, Dawid Weiss, Stanisław Osiński.
 * All rights reserved.
 *
 * Refer to the full license file "carrot2.LICENSE"
 * in the root folder of the repository checkout or at:
 * https://www.carrot2.org/carrot2.LICENSE
 */
package org.carrot2.math;

/**
 * A simple utility for calculating linear approximations based on values for equally distributed
 * points between minimum and maximum arguments.
 */
public class LinearApproximation {
  /** Values to base the approximation on */
  private double[] points;

  /** Minimum argument value */
  private double argMin;

  /** Maximum argument value */
  private double argMax;

  /** Step between value points */
  private double step;

  /** Argument value ranges */
  private double[] arguments;

  public LinearApproximation(double[] points, double argMin, double argMax) {
    this.points = points;
    this.argMin = argMin;
    this.argMax = argMax;

    arguments = new double[points.length];
    step = (argMax - argMin) / (points.length - 1);

    for (int i = 0; i < arguments.length; i++) {
      arguments[i] = argMin + step * i;
    }
  }

  /** Returns approximated value for the provided argument. */
  public double getValue(double argument) {
    if (points.length == 1) {
      return points[0];
    }

    if (argument <= arguments[0]) {
      return points[0];
    } else if (argument >= arguments[arguments.length - 1]) {
      return points[points.length - 1];
    } else {
      int bucket = (int) ((points.length - 1) * (argument - argMin) / (argMax - argMin));
      return points[bucket]
          + ((argument - arguments[bucket]) / step) * (points[bucket + 1] - points[bucket]);
    }
  }
}