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

.. only:: html

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

        :ref:`Go to the end <sphx_glr_download_auto_examples_svm_plot_svm_margin.py>`
        to download the full example code. or to run this example in your browser via Binder

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

.. _sphx_glr_auto_examples_svm_plot_svm_margin.py:


=========================================================
SVM 边界示例
=========================================================
下图说明了参数 `C` 对分隔线的影响。 `C` 的值较大时，基本上告诉我们的模型我们对数据的分布没有太多信心，只会考虑靠近分隔线的点。

 `C` 的值较小时，会包含更多/所有的观测值，允许使用该区域内的所有数据来计算边界。

.. GENERATED FROM PYTHON SOURCE LINES 10-84



.. rst-class:: sphx-glr-horizontal


    *

      .. image-sg:: /auto_examples/svm/images/sphx_glr_plot_svm_margin_001.png
         :alt: plot svm margin
         :srcset: /auto_examples/svm/images/sphx_glr_plot_svm_margin_001.png
         :class: sphx-glr-multi-img

    *

      .. image-sg:: /auto_examples/svm/images/sphx_glr_plot_svm_margin_002.png
         :alt: plot svm margin
         :srcset: /auto_examples/svm/images/sphx_glr_plot_svm_margin_002.png
         :class: sphx-glr-multi-img





.. code-block:: Python


    # 代码来源：Gaël Varoquaux
    # 由Jaques Grobler修改用于文档
    # SPDX许可证标识符：BSD-3-Clause

    import matplotlib.pyplot as plt
    import numpy as np

    from sklearn import svm

    # 我们创建了40个可分离点
    np.random.seed(0)
    X = np.r_[np.random.randn(20, 2) - [2, 2], np.random.randn(20, 2) + [2, 2]]
    Y = [0] * 20 + [1] * 20

    # 图号
    fignum = 1

    # 拟合模型
    for name, penalty in (("unreg", 1), ("reg", 0.05)):
        clf = svm.SVC(kernel="linear", C=penalty)
        clf.fit(X, Y)

        # 获取分离超平面
        w = clf.coef_[0]
        a = -w[0] / w[1]
        xx = np.linspace(-5, 5)
        yy = a * xx - (clf.intercept_[0]) / w[1]

        # 绘制通过支持向量的平行于分离超平面的直线（在垂直于超平面的方向上距离超平面一个边距）。在二维中，这个距离是垂直方向上的 sqrt(1+a^2)。
        margin = 1 / np.sqrt(np.sum(clf.coef_**2))
        yy_down = yy - np.sqrt(1 + a**2) * margin
        yy_up = yy + np.sqrt(1 + a**2) * margin

        # 绘制直线、点和最近的向量到平面
        plt.figure(fignum, figsize=(4, 3))
        plt.clf()
        plt.plot(xx, yy, "k-")
        plt.plot(xx, yy_down, "k--")
        plt.plot(xx, yy_up, "k--")

        plt.scatter(
            clf.support_vectors_[:, 0],
            clf.support_vectors_[:, 1],
            s=80,
            facecolors="none",
            zorder=10,
            edgecolors="k",
        )
        plt.scatter(
            X[:, 0], X[:, 1], c=Y, zorder=10, cmap=plt.get_cmap("RdBu"), edgecolors="k"
        )

        plt.axis("tight")
        x_min = -4.8
        x_max = 4.2
        y_min = -6
        y_max = 6

        YY, XX = np.meshgrid(yy, xx)
        xy = np.vstack([XX.ravel(), YY.ravel()]).T
        Z = clf.decision_function(xy).reshape(XX.shape)

        # 将结果放入轮廓图中
        plt.contourf(XX, YY, Z, cmap=plt.get_cmap("RdBu"), alpha=0.5, linestyles=["-"])

        plt.xlim(x_min, x_max)
        plt.ylim(y_min, y_max)

        plt.xticks(())
        plt.yticks(())
        fignum = fignum + 1

    plt.show()


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

   **Total running time of the script:** (0 minutes 0.033 seconds)


.. _sphx_glr_download_auto_examples_svm_plot_svm_margin.py:

.. only:: html

  .. container:: sphx-glr-footer sphx-glr-footer-example

    .. container:: binder-badge

      .. image:: images/binder_badge_logo.svg
        :target: https://mybinder.org/v2/gh/scikit-learn/scikit-learn/main?urlpath=lab/tree/notebooks/auto_examples/svm/plot_svm_margin.ipynb
        :alt: Launch binder
        :width: 150 px

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

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

    .. container:: sphx-glr-download sphx-glr-download-python

      :download:`Download Python source code: plot_svm_margin.py <plot_svm_margin.py>`

    .. container:: sphx-glr-download sphx-glr-download-zip

      :download:`Download zipped: plot_svm_margin.zip <plot_svm_margin.zip>`


.. include:: plot_svm_margin.recommendations


.. only:: html

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

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.github.io>`_