text: Curve with error band¶
  This example illustrates how to draw an error band around a parametrized curve.
  A parametrized curve x(t), y(t) can directly be drawn using
  plot.
  Out:
  [None]
  An error band can be used to indicate the uncertainty of the curve. In this example we assume that the error can be given as a scalar err that describes the uncertainty perpendicular to the curve in every point.
  We visualize this error as a colored band around the path using a
  PathPatch. The patch is created from two path segments (xp, yp), and
  (xn, yn) that are shifted by +/- err perpendicular to the curve (x, y).
  Note: This method of using a
  PathPatch is suited to arbitrary curves in
  2D. If you just have a standard y-vs.-x plot, you can use the simpler
  fill_between method (see also
  Filling the area between lines).
  def draw_error_band(ax, x, y, err, **kwargs): # Calculate normals via centered finite differences (except the first point # which uses a forward difference and the last point which uses a backward # difference). dx = np.concatenate([[x[1] - x[0]], x[2:] - x[:-2], [x[-1] - x[-2]]]) dy = np.concatenate([[y[1] - y[0]], y[2:] - y[:-2], [y[-1] - y[-2]]]) l = np.hypot(dx, dy) nx = dy / l ny = -dx / l # end points of errors xp = x + nx * err yp = y + ny * err xn = x - nx * err yn = y - ny * err vertices = np.block([[xp, xn[::-1]], [yp, yn[::-1]]]).T codes = np.full(len(vertices), Path.LINETO) codes[0] = codes[len(xp)] = Path.MOVETO path = Path(vertices, codes) ax.add_patch(PathPatch(path, **kwargs)) axs = (plt.figure(constrained_layout=True) .subplots(1, 2, sharex=True, sharey=True)) errs = [ (axs[0], "constant error", 0.05), (axs[1], "variable error", 0.05 * np.sin(2 * t) ** 2 + 0.04), ] for i, (ax, title, err) in enumerate(errs): ax.set(title=title, aspect=1, xticks=[], yticks=[]) ax.plot(x, y, "k") draw_error_band(ax, x, y, err=err, facecolor=f"C{i}", edgecolor="none", alpha=.3) plt.show()
  References
  The use of the following functions, methods, classes and modules is shown in this example:
  Keywords: matplotlib code example, codex, python plot, pyplot Gallery generated by Sphinx-Gallery