void window::exportDocument()
{
#ifndef QT_NO_PRINTER
    QString fileName = "mutual_inf.pdf";
#else
    QString fileName = "mutual_inf.png";
#endif

#ifndef QT_NO_FILEDIALOG
    const QList<QByteArray> imageFormats =
        QImageWriter::supportedImageFormats();

    QStringList filter;
    filter += "PDF Documents (*.pdf)";
#ifndef QWT_NO_SVG
    filter += "SVG Documents (*.svg)";
#endif
    filter += "Postscript Documents (*.ps)";

    if ( imageFormats.size() > 0 )
    {
        QString imageFilter("Images (");
        for ( int i = 0; i < imageFormats.size(); i++ )
        {
            if ( i > 0 )
                imageFilter += " ";
            imageFilter += "*.";
            imageFilter += imageFormats[i];
        }
        imageFilter += ")";

        filter += imageFilter;
    }

    fileName = QFileDialog::getSaveFileName(
        this, "Export File Name", fileName,
        filter.join(";;"), NULL, QFileDialog::DontConfirmOverwrite);
#endif

    if ( !fileName.isEmpty() )
    {
        QwtPlotRenderer renderer;
#if 0
        // flags to make the document look like the widget
        renderer.setDiscardFlag(QwtPlotRenderer::DiscardBackground, false);
        renderer.setLayoutFlag(QwtPlotRenderer::KeepMargins, true);
        renderer.setLayoutFlag(QwtPlotRenderer::KeepFrames, true);
#endif
        renderer.renderDocument(plot_mutualinf, fileName, QSizeF(300, 200), 85);
    }
}