
.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "gallery/lines_bars_and_markers/curve_error_band.py"
.. LINE NUMBERS ARE GIVEN BELOW.

.. only:: html

    .. note::
        :class: sphx-glr-download-link-note

        Click :ref:`here <sphx_glr_download_gallery_lines_bars_and_markers_curve_error_band.py>`
        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`.

.. GENERATED FROM PYTHON SOURCE LINES 10-27

.. 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





.. GENERATED FROM PYTHON SOURCE LINES 29-41

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`).

.. GENERATED FROM PYTHON SOURCE LINES 41-72

.. 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





.. GENERATED FROM PYTHON SOURCE LINES 73-80

------------

References
""""""""""

The use of the following functions, methods and classes is shown
in this example:

.. GENERATED FROM PYTHON SOURCE LINES 81-85

.. code-block:: default


    import matplotlib
    matplotlib.patches.PathPatch
    matplotlib.path.Path








.. rst-class:: sphx-glr-timing

   **Total running time of the script:** ( 0 minutes  1.476 seconds)


.. _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 <curve_error_band.py>`



  .. container:: sphx-glr-download sphx-glr-download-jupyter

     :download:`Download Jupyter notebook: curve_error_band.ipynb <curve_error_band.ipynb>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    Keywords: matplotlib code example, codex, python plot, pyplot
    `Gallery generated by Sphinx-Gallery
    <https://sphinx-gallery.readthedocs.io>`_
