Octave plot from Qt C++ application

Question

I have a QT C++ application that runs the Octave program using QProcess. I am able to communicate with it by reading the standard output/error and writing to it's standard input using write method (for example: octave->write("5 + 5\n");).

As I told you I get response from octave (from the above example I get "ans = 10").

However, when the command I write to Octave standard input has a "plot" (for example, a simple plot([1 2 3 4 5]);), the actual graphic is never shown. I know Octave runs gnuplot, I have it installed, and gnuplot_x11 too. I even change the gnuplot binary path in my Octave process by executing gnuplot_binary("/usr/bin/gnuplot"); from MY APPLICATION. I know it runs good because if I retrieve the new value I get it right. But I don't know why Octave doesn't show the graphic.

Here I start octave:

QStringList arguments;
arguments << "--persist";
octave->setProcessChannelMode(QProcess::MergedChannels);
octave->start("/usr/bin/octave", arguments);

Here I write commands to octave process:

if (octave->state() == QProcess::Running) {
    QString command = widget.txtInput->toPlainText();
    if (command.isEmpty()) {
        return;
    }
    command += "\n";
    octave->write(command.toAscii());
}

With this I print the octave response to a text edit:

widget.txtOutput->append(octave->readAll() + "\n");

And finally, I use this when the octave process starts:

QString gnuplot_path(tr("\"/usr/bin/gnuplot\""));
QString gnuplot_cmd(tr("gnuplot_binary(%1)\n").arg(gnuplot_path));
octave->write(gnuplot_cmd.toAscii());

I will appreciate any help you could give me.

Thanks in advance.

ypnos · Accepted Answer · 2011-04-11 11:42:18Z

3

Octave, like Matlab, can be run in batch mode to perform computations without graphical UI. I assume that Octave detects that it is not run from an interactive session, and therefore automatically goes into batch mode. You would expect Octave to suppress graphical output (e.g. gnuplot output) when being in batch mode.

Try to force Octave into interactive mode by using the --interactive command line option: http://www.gnu.org/software/octave/doc/interpreter/Command-Line-Options.html

edited Apr 11, 2011 at 11:42

answered Apr 11, 2011 at 11:36

ypnos

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1 Comment

Holland Salazar Over a year ago

Thank you so much for your answer... it worked! And now I understand octave a little bit more...

greg · Accepted Answer · 2011-05-09 00:19:58Z

1

I know you probably already solved your problem but this might be helpful for other... You can try to add a command to save your plot in a temporary folder in your octave request. Then display the graph in your ap

answered May 9, 2011 at 0:19

greg

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1 Comment

ypnos Over a year ago

Actually a good idea if you want better control of the display of the data.

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