code: public static PlotCanvas plot(double[][] z) {
          double[] lowerBound = {0, 0};
          double[] upperBound = {z[0].length, z.length};
          PlotCanvas canvas = new PlotCanvas(lowerBound, upperBound, false);
          canvas.add(new Contour(z));
  
          canvas.getAxis(0).setLabelVisible(false);
          canvas.getAxis(1).setLabelVisible(false);
  
          return canvas;
      }
docs: Create a plot canvas with the contour plot of given data.
  @param z a matrix.