}

  /** Returns whether this is a vertical transformation. */
  public abstract boolean isVertical();

  /** Returns whether this is a horizontal transformation. */
  public abstract boolean isHorizontal();

  /**
   * Returns the slope of the transformation, i.e. the rate of change of {@code y} with respect to
   * {@code x}. This must not be called on a vertical transformation (i.e. when {@link

    double x = 1.2;
    LinearTransformation transformation = LinearTransformation.vertical(x);
    assertVerticalLinearTransformation(transformation, x);
  }

  public void testVertical_infiniteX() {
    assertThrows(
        IllegalArgumentException.class,
        () -> LinearTransformation.vertical(Double.NEGATIVE_INFINITY));
  }

  public void testVertical_nanX() {

    double x = 1.2;
    LinearTransformation transformation = LinearTransformation.vertical(x);
    assertVerticalLinearTransformation(transformation, x);
  }

  public void testVertical_infiniteX() {
    assertThrows(
        IllegalArgumentException.class,
        () -> LinearTransformation.vertical(Double.NEGATIVE_INFINITY));
  }

  public void testVertical_nanX() {

    checkArgument(xDelta != 0.0);
    checkArgument(yDelta != 0.0);
    assertThat(transformation.isHorizontal()).isFalse();
    assertThat(transformation.isVertical()).isFalse();
    assertThat(transformation.inverse().isHorizontal()).isFalse();
    assertThat(transformation.inverse().isVertical()).isFalse();
    assertThat(transformation.transform(x1)).isWithin(ALLOWED_ERROR).of(y1);

    /** WAVE DASH */
    public static final char WAVE_DASH = '\u301C';

    /** FULLWIDTH TILDE */
    public static final char FULLWIDTH_TILDE = '\uFF5E';

    /** DOUBLE VERTICAL LINE */
    public static final char DOUBLE_VERTICAL_LINE = '\u2016';

    /** PARALLEL TO */
    public static final char PARALLEL_TO = '\u2225';

    /** MINUS SIGN */
    public static final char MINUS_SIGN = '\u2212';

-item-text{display:block;padding:.25rem 1.5rem;color:#212529}.btn-group,.btn-group-vertical{position:relative;display:-ms-inline-flexbox;display:inline-flex;vertical-align:middle}.btn-group-vertical>.btn,.btn-group>.btn{position:relative;-ms-flex:1 1 auto;flex:1 1 auto}.btn-group-vertical>.btn:hover,.btn-group>.btn:hover{z-index:1}.btn-group-vertical>.btn.active,.btn-group-vertical>.btn:active,.btn-group-vertical>.btn:focus,.btn-group>.btn.active,.btn-group>.btn:active,.btn-group>.btn:focus{z-in...

        HORIZONTAL_VALUES_PAIRED_STATS.leastSquaresFit(),
        HORIZONTAL_VALUES_PAIRED_STATS.yStats().mean());
    assertVerticalLinearTransformation(
        VERTICAL_VALUES_PAIRED_STATS.leastSquaresFit(),
        VERTICAL_VALUES_PAIRED_STATS.xStats().mean());
    assertThrows(IllegalStateException.class, () -> CONSTANT_VALUES_PAIRED_STATS.leastSquaresFit());
  }

  public void testEqualsAndHashCode() {

        HORIZONTAL_VALUES_PAIRED_STATS.leastSquaresFit(),
        HORIZONTAL_VALUES_PAIRED_STATS.yStats().mean());
    assertVerticalLinearTransformation(
        VERTICAL_VALUES_PAIRED_STATS.leastSquaresFit(),
        VERTICAL_VALUES_PAIRED_STATS.xStats().mean());
    assertThrows(IllegalStateException.class, () -> CONSTANT_VALUES_PAIRED_STATS.leastSquaresFit());
  }

  public void testEqualsAndHashCode() {

   * xStats().populationVariance() > 0.0 || yStats().populationVariance() > 0.0}). The result is
   * guaranteed to be horizontal if there is variance in the {@code x} data but not the {@code y}
   * data, and vertical if there is variance in the {@code y} data but not the {@code x} data.
   *
   * <p>This fit minimizes the root-mean-square error in {@code y} as a function of {@code x}. This

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