code: public static PlotCanvas plot(double[] x, double[] y, double[][] z) {
          double[] lowerBound = {Math.min(x), Math.min(y)};
          double[] upperBound = {Math.max(x), Math.max(y)};
          PlotCanvas canvas = new PlotCanvas(lowerBound, upperBound, false);
          canvas.add(new Heatmap(x, y, z));
  
          canvas.getAxis(0).setGridVisible(false);
          canvas.getAxis(1).setGridVisible(false);
  
          return canvas;
      }
docs: Create a plot canvas with the pseudo heat map plot of given data.
  @param x x coordinate of data matrix cells. Must be in ascending order.
  @param y y coordinate of data matrix cells. Must be in ascending order.
  @param z a data matrix to be shown in pseudo heat map.