Next: , Previous: Multiple Plot Windows, Up: Plotting

### 17.7 Low-Level plotting commands

— Command: gplot ranges expression using title style

Generate a 2-dimensional plot.

The ranges, using, title, and style arguments are optional, and the using, title and style qualifiers may appear in any order after the expression. You may plot multiple expressions with a single command by separating them with commas. Each expression may have its own set of qualifiers.

The optional item ranges has the syntax

```          [ x_lo : x_up ] [ y_lo : y_up ]
```

and may be used to specify the ranges for the axes of the plot, independent of the actual range of the data. The range for the y axis and any of the individual limits may be omitted. A range `[:]` indicates that the default limits should be used. This normally means that a range just large enough to include all the data points will be used.

The expression to be plotted must not contain any literal matrices (e.g. `[ 1, 2; 3, 4 ]`) since it is nearly impossible to distinguish a plot range from a matrix of data.

See the help for `gnuplot` for a description of the syntax for the optional items.

By default, the `gplot` command plots the second column of a matrix versus the first. If the matrix only has one column, it is taken as a vector of y-coordinates and the x-coordinate is taken as the element index, starting with zero. For example,

```          gplot rand (100,1) with linespoints
```

will plot 100 random values and connect them with lines. When `gplot` is used to plot a column vector, the indices of the elements are taken as x values.

If there are more than two columns, you can choose which columns to plot with the using qualifier. For example, given the data

```          x = (-10:0.1:10)';
data = [x, sin(x), cos(x)];
```

the command

```          gplot [-11:11] [-1.1:1.1] \
data with lines, data using 1:3 with impulses
```

will plot two lines. The first line is generated by the command `data with lines`, and is a graph of the sine function over the range −10 to 10. The data is taken from the first two columns of the matrix because columns to plot were not specified with the using qualifier.

The clause `using 1:3` in the second part of this plot command specifies that the first and third columns of the matrix `data` should be taken as the values to plot.

In this example, the ranges have been explicitly specified to be a bit larger than the actual range of the data so that the curves do not touch the border of the plot.

— Command: gsplot ranges expression using title style

Generate a 3-dimensional plot.

The ranges, using, title, and style arguments are optional, and the using, title and style qualifiers may appear in any order after the expression. You may plot multiple expressions with a single command by separating them with commas. Each expression may have its own set of qualifiers.

The optional item ranges has the syntax

```          [ x_lo : x_up ] [ y_lo : y_up ] [ z_lo : z_up ]
```

and may be used to specify the ranges for the axes of the plot, independent of the actual range of the data. The range for the y and z axes and any of the individual limits may be omitted. A range `[:]` indicates that the default limits should be used. This normally means that a range just large enough to include all the data points will be used.

The expression to be plotted must not contain any literal matrices (e.g. `[ 1, 2; 3, 4 ]`) since it is nearly impossible to distinguish a plot range from a matrix of data.

See the help for `gnuplot` for a description of the syntax for the optional items.

By default, the `gsplot` command plots each column of the expression as the z value, using the row index as the x value, and the column index as the y value. The indices are counted from zero, not one. For example,

```          gsplot rand (5, 2)
```

will plot a random surface, with the x and y values taken from the row and column indices of the matrix.

If parametric plotting mode is set (using the command gset parametric, then `gsplot` takes the columns of the matrix three at a time as the x, y and z values that define a line in three space. Any extra columns are ignored, and the x and y values are expected to be sorted. For example, with `parametric` set, it makes sense to plot a matrix like

```          1 1 3 2 1 6 3 1 9
1 2 2 2 2 5 3 2 8
1 3 1 2 3 4 3 3 7
```

but not `rand (5, 30)`.

— Command: gset options
— Command: gshow options
— Command: replot options

In addition to the basic plotting commands, the whole range of `gset` and `gshow` commands from `gnuplot` are available, as is `replot`.

Note that in Octave 2.0, the `set` and `show` commands were renamed to `gset` and `gshow` in order to allow for compatibility with the Matlab graphics and GUI commands in a future version of Octave. (For now, the old `set` and `show` commands do work, but they print an annoying warning message to try to get people to switch to using `gset` and `gshow`.)

The `gset` and `gshow` commands allow you to set and show `gnuplot` parameters. For more information about the `gset` and `gshow` commands, see the documentation for `set` and `show` in the `gnuplot` user's guide (also available on line if you run `gnuplot` directly, instead of running it from Octave).

The `replot` command allows you to force the plot to be redisplayed. This is useful if you have changed something about the plot, such as the title or axis labels. The `replot` command also accepts the same arguments as `gplot` or `gsplot` (except for data ranges) so you can add additional lines to existing plots.

For example,

```          gset term tek40
gset output "/dev/plotter"
gset title "sine with lines and cosine with impulses"
replot "sin (x) w l"
```

will change the terminal type for plotting, add a title to the current plot, add a graph of sin (x) to the plot, and force the new plot to be sent to the plot device. This last step is normally required in order to update the plot. This default is reasonable for slow terminals or hardcopy output devices because even when you are adding additional lines with a replot command, gnuplot always redraws the entire plot, and you probably don't want to have a completely new plot generated every time something as minor as an axis label changes.

The command `shg` is equivalent to executing `replot` without any arguments.

— Built-in Variable: automatic_replot

You can tell Octave to redisplay the plot each time anything about it changes by setting the value of the builtin variable `automatic_replot` to a nonzero value. Although it is fairly inefficient, especially for large plots, the default value is 1 for compatibility with Matlab.

Note that NaN values in the plot data are automatically omitted, and Inf values are converted to a very large value before calling gnuplot.