* <p>Special cases:
   *
   * <ul>
   *   <li>If {@code x} is NaN or less than zero, the result is NaN.
   *   <li>If {@code x} is positive infinity, the result is positive infinity.
   *   <li>If {@code x} is positive or negative zero, the result is negative infinity.
   * </ul>
   *
   * <p>The computed result is within 1 ulp of the exact result.
   *

   * contains both {@link Double#POSITIVE_INFINITY} and {@link Double#NEGATIVE_INFINITY} then the
   * result is {@link Double#NaN}. If it contains {@link Double#POSITIVE_INFINITY} and finite values
   * only or {@link Double#POSITIVE_INFINITY} only, the result is {@link Double#POSITIVE_INFINITY}.
   * If it contains {@link Double#NEGATIVE_INFINITY} and finite values only or {@link

   * times, due to numerical errors.
   *
   * <h3>Non-finite values</h3>
   *
   * <p>If the dataset contains any non-finite values ({@link Double#POSITIVE_INFINITY}, {@link
   * Double#NEGATIVE_INFINITY}, or {@link Double#NaN}) then the result is {@link Double#NaN}.
   *
   * @throws IllegalStateException if the dataset is empty
   */
  public double populationCovariance() {

  }

  public void testLog2Zero() {
    assertEquals(Double.NEGATIVE_INFINITY, DoubleMath.log2(0.0));
    assertEquals(Double.NEGATIVE_INFINITY, DoubleMath.log2(-0.0));
  }

  public void testLog2NaNInfinity() {
    assertEquals(Double.POSITIVE_INFINITY, DoubleMath.log2(Double.POSITIVE_INFINITY));
    assertTrue(Double.isNaN(DoubleMath.log2(Double.NEGATIVE_INFINITY)));
    assertTrue(Double.isNaN(DoubleMath.log2(Double.NaN)));
  }

    assertThrows(
        IllegalArgumentException.class,
        () -> LinearTransformation.mapping(Double.POSITIVE_INFINITY, 3.4));
  }

  public void testMapping_infiniteY1() {
    assertThrows(
        IllegalArgumentException.class,
        () -> LinearTransformation.mapping(1.2, Double.NEGATIVE_INFINITY));
  }

  public void testMappingAnd_infiniteX2() {
    assertThrows(
        IllegalArgumentException.class,

    assertThrows(
        IllegalArgumentException.class,
        () -> LinearTransformation.mapping(Double.POSITIVE_INFINITY, 3.4));
  }

  public void testMapping_infiniteY1() {
    assertThrows(
        IllegalArgumentException.class,
        () -> LinearTransformation.mapping(1.2, Double.NEGATIVE_INFINITY));
  }

  public void testMappingAnd_infiniteX2() {
    assertThrows(
        IllegalArgumentException.class,

          return Double.MAX_VALUE * sign(x);
        case FLOOR:
          return (roundArbitrarily == Double.POSITIVE_INFINITY)
              ? Double.MAX_VALUE
              : Double.NEGATIVE_INFINITY;
        case CEILING:
          return (roundArbitrarily == Double.POSITIVE_INFINITY)
              ? Double.POSITIVE_INFINITY
              : -Double.MAX_VALUE;
        case UP:
          return roundArbitrarily;
        case UNNECESSARY:

   * contains both {@link Double#POSITIVE_INFINITY} and {@link Double#NEGATIVE_INFINITY} then the
   * result is {@link Double#NaN}. If it contains {@link Double#POSITIVE_INFINITY} and finite values
   * only or {@link Double#POSITIVE_INFINITY} only, the result is {@link Double#POSITIVE_INFINITY}.
   * If it contains {@link Double#NEGATIVE_INFINITY} and finite values only or {@link

            2, POSITIVE_INFINITY,
            8, POSITIVE_INFINITY,
            9, POSITIVE_INFINITY, // interpolating between two POSITIVE_INFINITY values
            10, POSITIVE_INFINITY);
  }

  public void testScale_indexes_varargs_compute_doubleCollection_nan() {
    assertThat(Quantiles.scale(10).indexes(0, 1, 2, 8, 9, 10).compute(ONE_TO_FIVE_AND_NAN))

            2, POSITIVE_INFINITY,
            8, POSITIVE_INFINITY,
            9, POSITIVE_INFINITY, // interpolating between two POSITIVE_INFINITY values
            10, POSITIVE_INFINITY);
  }

  public void testScale_indexes_varargs_compute_doubleCollection_nan() {
    assertThat(Quantiles.scale(10).indexes(0, 1, 2, 8, 9, 10).compute(ONE_TO_FIVE_AND_NAN))