# Documentation

## Create Graph with Two y-Axes

This example shows how to create a graph with two y-axes, label the axes, and display the grid lines.

Create and Plot Data

Create the data.

```A = 1000; a = 0.005; b = 0.005; t = 0:900; z1 = A*exp(-a*t); z2 = sin(b*t); ```

Use `plotyy` to create a graph with two y-axes. Plot `z1` versus `t` using semilogarithmic scaling. Plot `z2` versus `t` using linear scaling. Return the two axes in array `ax`, and return the two lines as `p1` and `p2`.

```[ax,p1,p2] = plotyy(t,z1,t,z2,'semilogy','plot'); ```

The left y-axis corresponds to the first set of data plotted, which is the semilogarithmic plot for `z1`. The first axes, `ax(1)`, and the line, `p1`, correspond to the first set of data.

The right y-axis corresponds to the second set of data plotted, which is the line plot for `z2`. The second axes, `ax(2)`, and the line, `p2`, correspond to the second set of data.

Label the Axes

Label the left y-axis by passing the first axes to the `ylabel` function. Then, label the right y-axis by passing the second axes to the `ylabel` function. Label the x-axis using either axes.

```ylabel(ax(1),'Semilog Plot') % label left y-axis ylabel(ax(2),'Linear Plot') % label right y-axis xlabel(ax(2),'Time') % label x-axis ```

Modify Line Appearance

Change the appearance of the lines. Starting in R2014b, you can use dot notation to set properties. If you are using an earlier release, use the `set` function instead.

```p1.LineStyle = '--'; p1.LineWidth = 2; p2.LineWidth = 2; ```

Display Grid Lines

Display the log grid associated with the left y-axis by passing the first axes to the `grid` function.

```grid(ax(1),'on') ```

To display the linear grid associated with the right y-axis instead, use `grid(ax(2),'on')`.