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 Contour(x, y, z));
  
          return canvas;
      }
docs: Create a plot canvas with the contour plot of given data.
  @param z a matrix.