# refline

Add reference line to plot

## Syntax

`refline(m,b)refline(coeffs)reflinerefline(ax,___)hline = refline(___)`

## Description

`refline(m,b)` adds a reference line with slope `m` and intercept `b` to the current axes.

`refline(coeffs)`, where `coeffs` is a two-element coefficient vector, adds the line

` y = coeffs(1)*x + coeffs(2) `

to the figure.

`refline` with no input arguments is equivalent to `lsline`.

`refline(ax,___)` adds a reference line to the plot in the axis specified by `ax`, using any of the previous syntaxes.

`hline = refline(___)` returns the handle `hline` to the line.

## Examples

collapse all

### Add a Reference Line at the Mean

Generate sample data for independent variable `x` and a dependent variable `y` .

```x = 1:10; y = x + randn(1,10); ```

Create a scatter plot of `x` and `y` .

```scatter(x,y,25,'b','*') ```

Superimpose a least-squares line on the scatter plot.

```lsline ```

Add a reference line at the mean of the scatter and its least-squares line.

```mu = mean(y); hline = refline([0 mu]); hline.Color = 'r'; ```

The red line shows the reference line at the mean of data.

### Specify Axes for Least-Squares and Reference Lines

Define the x-variable and two different y-variables to use for the plots.

```rng default % For reproducibility x = 1:10; y1 = x + randn(1,10); y2 = 2*x + randn(1,10); ```

Define `ax1` as the top half of the figure, and `ax2` as the bottom half of the figure. Create the first scatter plot on the top axis using `y1`, and the second scatter plot on the bottom axis using `y2`.

```figure ax1 = subplot(2,1,1); ax2 = subplot(2,1,2); scatter(ax1,x,y1) scatter(ax2,x,y2) ```

Superimpose a least-squares line on the top plot, and a reference line at the mean of the `y2` values in the bottom plot.

```lsline(ax1) mu = mean(y2); refline(ax2,[0 mu]) ```