预备知识

2.4 微积分

2.4.1 导数和微分（绘制图像部分代码

查看代码

import numpy as np
import matplotlib.pyplot as plt
from d2l import torch as d2l


def f(x):
    return 3 * x ** 2 - 4 * x

def set_figsize(figsize=(3.5, 2.5)):
    plt.rcParams['figure.figsize'] = figsize

def set_axes(axes, xlabel, ylabel, xlim, ylim, xscale, yscale, legend):
    axes.set_xlabel(xlabel)
    axes.set_ylabel(ylabel)
    axes.set_xscale(xscale)
    axes.set_yscale(yscale)
    axes.set_xlim(xlim)
    axes.set_ylim(ylim)
    if legend:
        axes.legend(legend)
    axes.grid()

def plot(X, Y=None, xlabel=None, ylabel=None, legend=None, xlim=None,
         ylim=None, xscale='linear', yscale='linear',
         fmts=('-', 'm--', 'g-.', 'r:'), figsize=(3.5, 2.5), axes=None):
    if legend is None:
        legend = []

    set_figsize(figsize)
    axes = axes if axes else plt.gca()

    def has_one_axis(X):
        return (hasattr(X, "ndim") and X.ndim == 1 or
                isinstance(X, list) and not hasattr(X[0], "__len__"))

    if has_one_axis(X):
        X = [X]
    if Y is None:
        X, Y = [[]] * len(X), X
    elif has_one_axis(Y):
        Y = [Y]
    if len(X) != len(Y):
        X = X * len(Y)
    axes.cla()
    for x, y, fmt in zip(X, Y, fmts):
        if len(x):
            axes.plot(x, y, fmt)
        else:
            axes.plot(y, fmt)
    set_axes(axes, xlabel, ylabel, xlim, ylim, xscale, yscale, legend)
    plt.show()

x = np.arange(0.1, 4, 0.1)
plot(x, [x ** 3 - 1.0 / x, 4 * (x - 1)], 'x', 'f(x)', legend=['f(x)', 'Tangent line (x=1)'], figsize=(5, 5))