@Test
 public void testHankelFunctionModule() throws IOException {
   JFreeChart chart = ChartBuilder.createModulePlot(function, "Hankel");
   ChartUtilities.saveChartAsPNG(new File(getPlotPath("module")), chart, 800, 600);
 }
 @Test
 public void testHankelFunctionArg() throws IOException {
   JFreeChart chart = ChartBuilder.createArgPlot(function, "Radially Symmetric");
   ChartUtilities.saveChartAsPNG(new File(getPlotPath("arg")), chart, 800, 600);
 }
 @Test
 public void testHankelFunctionPolarArg() throws IOException {
   BufferedImage image = ChartBuilder.createArgPolarPlot(function);
   ChartUtils.saveChartAsPNG(image, new File(getPlotPath("polar_arg")));
 }
 @Test
 public void testHankelFunctionPolar() throws IOException {
   BufferedImage chart = ChartBuilder.createModulePolarPlot(function);
   ChartUtils.saveChartAsPNG(chart, new File(getPlotPath("polar")));
 }