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16.1 Two-Dimensional Plotting

The basic plotting commands are:

— Function File: axes ()
— Function File: axes (property, value, ...)
— Function File: axes (h)

Create an axes object and return a handle to it.

— Function File: plot (args)

This function produces two-dimensional plots. Many different combinations of arguments are possible. The simplest form is

          plot (y)
     

where the argument is taken as the set of y coordinates and the x coordinates are taken to be the indices of the elements, starting with 1.

To save a plot, in one of several image formats such as PostScript or PNG, use the print command.

If more than one argument is given, they are interpreted as

          plot (x, y, fmt, ...)
     

or as

          plot (x, y, property, value, ...)
     

where y, fmt, property and value are optional, and any number of argument sets may appear. The x and y values are interpreted as follows:

If the fmt argument is supplied, it is interpreted as follows. If fmt is missing, the default gnuplot line style is assumed.

`-'
Set lines plot style (default).
`.'
Set dots plot style.
`^'
Set impulses plot style.
`L'
Set steps plot style.
`n'
Interpreted as the plot color if n is an integer in the range 1 to 6.
`nm'
If nm is a two digit integer and m is an integer in the range 1 to 6, m is interpreted as the point style. This is only valid in combination with the @ or -@ specifiers.
`c'
If c is one of "k" (black), "r" (red), "g" (green), "b" (blue), "m" (magenta), "c" (cyan), or "w" (white), it is interpreted as the line plot color.
`";title;"'
Here "title" is the label for the key.
`+'
`*'
`o'
`x'
Used in combination with the points or linespoints styles, set the point style.

The color line styles have the following meanings on terminals that support color.

          Number  Gnuplot colors  (lines)points style
            1       red                   *
            2       green                 +
            3       blue                  o
            4       magenta               x
            5       cyan                house
            6       brown            there exists
     

The fmt argument can also be used to assign key titles. To do so, include the desired title between semi-colons after the formatting sequence described above, e.g. "+3;Key Title;" Note that the last semi-colon is required and will generate an error if it is left out.

If a property is given it must be followed by value. The property value pairs are applied to the lines drawn by plot.

Here are some plot examples:

          plot (x, y, "@12", x, y2, x, y3, "4", x, y4, "+")
     

This command will plot y with points of type 2 (displayed as `+') and color 1 (red), y2 with lines, y3 with lines of color 4 (magenta) and y4 with points displayed as `+'.

          plot (b, "*", "markersize", 3)
     

This command will plot the data in the variable b, with points displayed as `*' with a marker size of 3.

          t = 0:0.1:6.3;
          plot (t, cos(t), "-;cos(t);", t, sin(t), "+3;sin(t);");
     

This will plot the cosine and sine functions and label them accordingly in the key.

     
     
See also: semilogx, semilogy, loglog, polar, mesh, contour, __pltopt__ bar, stairs, errorbar, xlabel, ylabel, title, print.

— Function File: line ()
— Function File: line (x, y)
— Function File: line (x, y, z)
— Function File: line (x, y, z, opts)

Create line object from x and y and insert in current axes object. Return handle to line object.

— Function File: fplot (fn, limits)
— Function File: fplot (fn, limits, tol)
— Function File: fplot (fn, limits, n)
— Function File: fplot (..., LineSpec)

Plot a function fn, within the defined limits. fn an be either a string, a function handle or an inline function. The limits of the plot are given by limits of the form [xlo, xhi] or [xlo, xhi, ylo, yhi]. tol is the default tolerance to use for the plot, and if tol is an integer it is assumed that it defines the number points to use in the plot. The LineSpec is passed to the plot command.

             fplot ("cos", [0, 2*pi])
             fplot ("[cos(x), sin(x)]", [0, 2*pi])
     
     
     
See also: plot.

— Function File: drawnow ()

Display the current graphics.

— Function File: shg

Show the graph window. Currently, this is the same as executing drawnow.

     
     
See also: plot, semilogx, semilogy, loglog, polar, mesh, contour, bar, stairs, xlabel, ylabel.

— Function File: hold args

Tell Octave to `hold' the current data on the plot when executing subsequent plotting commands. This allows you to execute a series of plot commands and have all the lines end up on the same figure. The default is for each new plot command to clear the plot device first. For example, the command

          hold on
     

turns the hold state on. An argument of "off" turns the hold state off, and hold with no arguments toggles the current hold state.

— Function File: ishold

Return 1 if the next line will be added to the current plot, or 0 if the plot device will be cleared before drawing the next line.

— Function File: newplot ()