* the arithmetic mean of the population.
   *
   * <h3>Non-finite values</h3>
   *
   * <p>If the dataset contains {@link Double#NaN} then the result is {@link Double#NaN}. If it
   * 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

          .that(Doubles.indexOf(new double[] {5.0, value, value, 5.0}, new double[] {value, value}))
          .isEqualTo(1);
    }
    assertThat(Doubles.indexOf(new double[] {5.0, NaN, NaN, 5.0}, new double[] {NaN, NaN}))
        .isEqualTo(-1);
  }

  public void testLastIndexOf() {
    assertThat(Doubles.lastIndexOf(EMPTY, 1.0)).isEqualTo(-1);
    assertThat(Doubles.lastIndexOf(ARRAY1, 2.0)).isEqualTo(-1);

   * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for
   * the returned list is unspecified.
   *
   * <p>The returned list may have unexpected behavior if it contains {@code NaN}, or if {@code NaN}
   * is used as a parameter to any of its methods.
   *
   * <p>The returned list is serializable.
   *
   * <p><b>Note:</b> when possible, you should represent your data as an {@link

        assertFalse(DoubleMath.fuzzyEquals(a, Double.NaN, tolerance));
        assertFalse(DoubleMath.fuzzyEquals(Double.NaN, a, tolerance));
      }
    }
  }

  public void testFuzzyEqualsTwoNaNs() {
    for (double tolerance : TOLERANCE_CANDIDATES) {
      assertTrue(DoubleMath.fuzzyEquals(Double.NaN, Double.NaN, tolerance));
    }
  }

  public void testFuzzyEqualsZeroTolerance() {

   *
   * <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() {
    checkState(count() != 0);
    return sumOfProductsOfDeltas / count();
  }

    }

    @Override
    public double slope() {
      return NaN;
    }

    @Override
    public double transform(double x) {
      return NaN;
    }

    @Override
    public LinearTransformation inverse() {
      return this;
    }

    @Override
    public String toString() {
      return "NaN";
    }
  }

   * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for
   * the returned list is unspecified.
   *
   * <p>The returned list may have unexpected behavior if it contains {@code NaN}, or if {@code NaN}
   * is used as a parameter to any of its methods.
   *
   * <p>The returned list is serializable.
   *
   * @param backingArray the array to back the list
   * @return a list view of the array
   */

          .that(Doubles.indexOf(new double[] {5.0, value, value, 5.0}, new double[] {value, value}))
          .isEqualTo(1);
    }
    assertThat(Doubles.indexOf(new double[] {5.0, NaN, NaN, 5.0}, new double[] {NaN, NaN}))
        .isEqualTo(-1);
  }

  public void testLastIndexOf() {
    assertThat(Doubles.lastIndexOf(EMPTY, 1.0)).isEqualTo(-1);
    assertThat(Doubles.lastIndexOf(ARRAY1, 2.0)).isEqualTo(-1);

      assertWithMessage("" + value)
          .that(Floats.indexOf(new float[] {5f, value, value, 5f}, new float[] {value, value}))
          .isEqualTo(1);
    }
    assertThat(Floats.indexOf(new float[] {5f, NaN, NaN, 5f}, new float[] {NaN, NaN}))
        .isEqualTo(-1);
  }

  public void testLastIndexOf() {
    assertThat(Floats.lastIndexOf(EMPTY, 1.0f)).isEqualTo(-1);
    assertThat(Floats.lastIndexOf(ARRAY1, 2.0f)).isEqualTo(-1);

      assertWithMessage("" + value)
          .that(Floats.indexOf(new float[] {5f, value, value, 5f}, new float[] {value, value}))
          .isEqualTo(1);
    }
    assertThat(Floats.indexOf(new float[] {5f, NaN, NaN, 5f}, new float[] {NaN, NaN}))
        .isEqualTo(-1);
  }

  public void testLastIndexOf() {
    assertThat(Floats.lastIndexOf(EMPTY, 1.0f)).isEqualTo(-1);
    assertThat(Floats.lastIndexOf(ARRAY1, 2.0f)).isEqualTo(-1);