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

.. only:: html

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

        Click :ref:`here <sphx_glr_download_gallery_images_contours_and_fields_pcolormesh_levels.py>`
        to download the full example code

.. rst-class:: sphx-glr-example-title

.. _sphx_glr_gallery_images_contours_and_fields_pcolormesh_levels.py:


==========
pcolormesh
==========

`.axes.Axes.pcolormesh` allows you to generate 2-D image-style plots.  Note it
is faster than the similar `~.axes.Axes.pcolor`.

.. GENERATED FROM PYTHON SOURCE LINES 10-17

.. code-block:: default


    import matplotlib
    import matplotlib.pyplot as plt
    from matplotlib.colors import BoundaryNorm
    from matplotlib.ticker import MaxNLocator
    import numpy as np








.. GENERATED FROM PYTHON SOURCE LINES 18-24

Basic pcolormesh
----------------

We usually specify a pcolormesh by defining the edge of quadrilaterals and
the value of the quadrilateral.  Note that here *x* and *y* each have one
extra element than Z in the respective dimension.

.. GENERATED FROM PYTHON SOURCE LINES 24-33

.. code-block:: default


    np.random.seed(19680801)
    Z = np.random.rand(6, 10)
    x = np.arange(-0.5, 10, 1)  # len = 11
    y = np.arange(4.5, 11, 1)  # len = 7

    fig, ax = plt.subplots()
    ax.pcolormesh(x, y, Z)




.. image:: /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_levels_001.png
    :alt: pcolormesh levels
    :class: sphx-glr-single-img


.. rst-class:: sphx-glr-script-out

 Out:

 .. code-block:: none


    <matplotlib.collections.QuadMesh object at 0x7f73b7833fa0>



.. GENERATED FROM PYTHON SOURCE LINES 34-39

Non-rectilinear pcolormesh
--------------------------

Note that we can also specify matrices for *X* and *Y* and have
non-rectilinear quadrilaterals.

.. GENERATED FROM PYTHON SOURCE LINES 39-49

.. code-block:: default


    x = np.arange(-0.5, 10, 1)  # len = 11
    y = np.arange(4.5, 11, 1)  # len = 7
    X, Y = np.meshgrid(x, y)
    X = X + 0.2 * Y  # tilt the coordinates.
    Y = Y + 0.3 * X

    fig, ax = plt.subplots()
    ax.pcolormesh(X, Y, Z)




.. image:: /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_levels_002.png
    :alt: pcolormesh levels
    :class: sphx-glr-single-img


.. rst-class:: sphx-glr-script-out

 Out:

 .. code-block:: none


    <matplotlib.collections.QuadMesh object at 0x7f73b6ca2160>



.. GENERATED FROM PYTHON SOURCE LINES 50-59

Centered Coordinates
---------------------

Often a user wants to pass *X* and *Y* with the same sizes as *Z* to
`.axes.Axes.pcolormesh`.  This is also allowed if ``shading='auto'`` is
passed (default set by :rc:`pcolor.shading`).  Pre Matplotlib 3.3,
``shading='flat'`` would drop the last column and row of *Z*; while that
is still allowed for back compatibility purposes, a DeprecationWarning is
raised.

.. GENERATED FROM PYTHON SOURCE LINES 59-70

.. code-block:: default


    x = np.arange(10)  # len = 10
    y = np.arange(6)  # len = 6
    X, Y = np.meshgrid(x, y)

    fig, axs = plt.subplots(2, 1, sharex=True, sharey=True)
    axs[0].pcolormesh(X, Y, Z, vmin=np.min(Z), vmax=np.max(Z), shading='auto')
    axs[0].set_title("shading='auto' = 'nearest'")
    axs[1].pcolormesh(X, Y, Z, vmin=np.min(Z), vmax=np.max(Z), shading='flat')
    axs[1].set_title("shading='flat'")




.. image:: /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_levels_003.png
    :alt: shading='auto' = 'nearest', shading='flat'
    :class: sphx-glr-single-img


.. rst-class:: sphx-glr-script-out

 Out:

 .. code-block:: none

    /build/matplotlib-eAPYn3/matplotlib-3.3.4/examples/images_contours_and_fields/pcolormesh_levels.py:67: MatplotlibDeprecationWarning: shading='flat' when X and Y have the same dimensions as C is deprecated since 3.3.  Either specify the corners of the quadrilaterals with X and Y, or pass shading='auto', 'nearest' or 'gouraud', or set rcParams['pcolor.shading'].  This will become an error two minor releases later.
      axs[1].pcolormesh(X, Y, Z, vmin=np.min(Z), vmax=np.max(Z), shading='flat')

    Text(0.5, 1.0, "shading='flat'")



.. GENERATED FROM PYTHON SOURCE LINES 71-78

Making levels using Norms
-------------------------

Shows how to combine Normalization and Colormap instances to draw
"levels" in `.axes.Axes.pcolor`, `.axes.Axes.pcolormesh`
and `.axes.Axes.imshow` type plots in a similar
way to the levels keyword argument to contour/contourf.

.. GENERATED FROM PYTHON SOURCE LINES 78-120

.. code-block:: default


    # make these smaller to increase the resolution
    dx, dy = 0.05, 0.05

    # generate 2 2d grids for the x & y bounds
    y, x = np.mgrid[slice(1, 5 + dy, dy),
                    slice(1, 5 + dx, dx)]

    z = np.sin(x)**10 + np.cos(10 + y*x) * np.cos(x)

    # x and y are bounds, so z should be the value *inside* those bounds.
    # Therefore, remove the last value from the z array.
    z = z[:-1, :-1]
    levels = MaxNLocator(nbins=15).tick_values(z.min(), z.max())


    # pick the desired colormap, sensible levels, and define a normalization
    # instance which takes data values and translates those into levels.
    cmap = plt.get_cmap('PiYG')
    norm = BoundaryNorm(levels, ncolors=cmap.N, clip=True)

    fig, (ax0, ax1) = plt.subplots(nrows=2)

    im = ax0.pcolormesh(x, y, z, cmap=cmap, norm=norm)
    fig.colorbar(im, ax=ax0)
    ax0.set_title('pcolormesh with levels')


    # contours are *point* based plots, so convert our bound into point
    # centers
    cf = ax1.contourf(x[:-1, :-1] + dx/2.,
                      y[:-1, :-1] + dy/2., z, levels=levels,
                      cmap=cmap)
    fig.colorbar(cf, ax=ax1)
    ax1.set_title('contourf with levels')

    # adjust spacing between subplots so `ax1` title and `ax0` tick labels
    # don't overlap
    fig.tight_layout()

    plt.show()




.. image:: /gallery/images_contours_and_fields/images/sphx_glr_pcolormesh_levels_004.png
    :alt: pcolormesh with levels, contourf with levels
    :class: sphx-glr-single-img





.. GENERATED FROM PYTHON SOURCE LINES 121-127

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

References
""""""""""

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

.. GENERATED FROM PYTHON SOURCE LINES 128-137

.. code-block:: default


    matplotlib.axes.Axes.pcolormesh
    matplotlib.pyplot.pcolormesh
    matplotlib.axes.Axes.contourf
    matplotlib.pyplot.contourf
    matplotlib.figure.Figure.colorbar
    matplotlib.pyplot.colorbar
    matplotlib.colors.BoundaryNorm
    matplotlib.ticker.MaxNLocator








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

   **Total running time of the script:** ( 0 minutes  2.354 seconds)


.. _sphx_glr_download_gallery_images_contours_and_fields_pcolormesh_levels.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: pcolormesh_levels.py <pcolormesh_levels.py>`



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

     :download:`Download Jupyter notebook: pcolormesh_levels.ipynb <pcolormesh_levels.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>`_
