.. only:: html .. note:: :class: sphx-glr-download-link-note Click :ref:`here ` to download the full example code .. rst-class:: sphx-glr-example-title .. _sphx_glr_gallery_lines_bars_and_markers_curve_error_band.py: ===================== 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 `~.Axes.plot`. .. code-block:: default import numpy as np from scipy.interpolate import splprep, splev import matplotlib.pyplot as plt from matplotlib.path import Path from matplotlib.patches import PathPatch N = 400 t = np.linspace(0, 2 * np.pi, N) r = 0.5 + np.cos(t) x, y = r * np.cos(t), r * np.sin(t) fig, ax = plt.subplots() ax.plot(x, y) plt.show() .. image:: /gallery/lines_bars_and_markers/images/sphx_glr_curve_error_band_001.png :alt: curve error band :class: sphx-glr-single-img 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 `~.Axes.fill_between` method (see also :doc:`/gallery/lines_bars_and_markers/fill_between_demo`). .. code-block:: default # Error amplitudes depending on the curve parameter *t* # (actual values are arbitrary and only for illustrative purposes): err = 0.05 * np.sin(2 * t) ** 2 + 0.04 + 0.02 * np.cos(9 * t + 2) # calculate normals via derivatives of splines tck, u = splprep([x, y], s=0) dx, dy = splev(u, tck, der=1) 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 = Path.LINETO * np.ones(len(vertices), dtype=Path.code_type) codes[0] = codes[len(xp)] = Path.MOVETO path = Path(vertices, codes) patch = PathPatch(path, facecolor='C0', edgecolor='none', alpha=0.3) fig, ax = plt.subplots() ax.plot(x, y) ax.add_patch(patch) plt.show() .. image:: /gallery/lines_bars_and_markers/images/sphx_glr_curve_error_band_002.png :alt: curve error band :class: sphx-glr-single-img ------------ References """""""""" The use of the following functions, methods and classes is shown in this example: .. code-block:: default import matplotlib matplotlib.patches.PathPatch matplotlib.path.Path .. _sphx_glr_download_gallery_lines_bars_and_markers_curve_error_band.py: .. only :: html .. container:: sphx-glr-footer :class: sphx-glr-footer-example .. container:: sphx-glr-download sphx-glr-download-python :download:`Download Python source code: curve_error_band.py ` .. container:: sphx-glr-download sphx-glr-download-jupyter :download:`Download Jupyter notebook: curve_error_band.ipynb ` .. only:: html .. rst-class:: sphx-glr-signature Keywords: matplotlib code example, codex, python plot, pyplot `Gallery generated by Sphinx-Gallery `_