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Thread: Octave plotting issue

  1. #1
    Join Date
    Nov 2007

    Octave plotting issue

    I am using octave to create a plot with two curves on it with a legend labeling each curve. The following code plots each curve and adds a label to the legend.

    plot(time_Ey,Ey_analytic,'b');	# add analytical vector to plot
    legend("Analytical Output");	# add label to legend
    hold on;			# hold on	
    plot(time_Ey,Ey(:,loc_D+1),'r');# add simulated vector to plot
    legend("Simulation Output");	# add label to legend
    hold off;			# hold off
    My problem is, this code works perfectly on my netbook but not on my desktop. The legend should have two entries; "Analytical Output" with a blue line next to it, and "Simulated Output" with a red line next to it. When I run it on my desktop, the legend only has only entry in it: "Simulated Output" with a blue line next to it. It seems like it is only processing the second legend command and linking it to the first plot command.

    Netbook Info: Ubuntu 10.04 Netbook
    Octave: version 3.2.3
    gnuplot: Version 4.2 patchlevel 6
    Desktop Info: Ubuntu 10.10 Desktop
    Octave: version 3.2.4
    gnuplot: version 4.4 patchlevel 0

    I have tried many different methods to get my desktop to produce a proper legend but I am out of ideas.
    I tried adding clf in the beginning, to clear the plot.
    I tried moving the hold command around.
    I tried using one legend command with the following code. It produced a legend with both entries, but put a blue line next to both.

    legend("Analytical Output","Simulated Output");
    I am stumped, any help or suggestions would be greatly appreciated. Thanks in advance.

  2. #2
    Join Date
    Nov 2007

    Re: Octave plotting issue

    I found some bug reports from others talking about a similar plotting issue.

    There is a new stable release of octave (octave3.4.0) but it doesn't seem to be available from the software center yet. I downloaded the tarball from and attempted to install it from source but I am confused about a dependency issue.

    I get the following warnings when I run the configure file.

    configure: WARNING: OpenGL libs (GL and GLU) not found. Native graphics will be disabled.
    configure: WARNING: 
    configure: WARNING: I didn't find the necessary libraries to compile native
    configure: WARNING: graphics.  It isn't necessary to have native graphics,
    configure: WARNING: but you will need to have gnuplot installed or you won't
    configure: WARNING: be able to use any of Octave's plotting commands
    Although, when I search for "OpenGL" in the software center, it says it is installed.

    My question is, what exactly is native graphics and if OpenGL is already installed, what am I missing?

    Thanks for the help.

  3. #3
    Join Date
    Nov 2007

    Re: Octave plotting issue

    Recent versions of Octave do not seem to support legend creation using the method in my original post. I figured I would share an alternative method and set this post as solved.

    Store all legend annotations in a cell array and call the legend function once with the cell array as the only argument.....

    x = linspace(1,20,10);	    # x-axis data
    y1 = linspace(5,10,10);	    # curve 1 data
    y2 = linspace(5,30,10);	    # curve 2 data
    legend_list = {"y1","y2"};  # cell array
    plot(x,y1,'b');		# add curve one to plot
    hold on;		# hold on	
    plot(x,y2,'r');		# add curve two to plot
    legend(legend_list);	# add legend entries for curve 1 and 2
    hold off;		# hold off

  4. #4
    Join Date
    Apr 2013

    Re: Octave plotting issue

    i'm trying to plot graphs with octave under ubuntu 12.04lts .It is possible to tape:
    octave input-file-name ?

    Thank you for your help.

  5. #5
    Join Date
    Nov 2007

    Re: Octave plotting issue

    To tape? I'm not sure I understand what you're asking. Could you be more descriptive?

    You can run octave scripts from the shell. Is that what you're asking? Take a look at the manual to see the octave.

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