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| import numpy as np from matplotlib_inline import backend_inline from d2l import torch as d2l
def f(x): return 3 * x ** 2 - 4 * x
def numerical_lim(f, x, delta): return (f(x + delta) - f(x)) / delta
def use_svg_display(): """使用svg格式在Jupyter中显示绘图""" backend_inline.set_matplotlib_formats('svg') def set_figsize(figsize=(3.5, 2.5)): """设置matplotlib的图表大小""" use_svg_display() d2l.plt.rcParams['figure.figsize'] = figsize def set_axes(axes, xlabel, ylabel, xlim, ylim, xscale, yscale, legend): """设置matplotlib的轴""" 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): """绘制数据点""" if legend is None: legend = [] set_figsize(figsize) axes = axes if axes else d2l.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) if __name__ == "__main__": delta = 1e-5 tangent = numerical_lim(f, 1, delta) print(f'delta={delta:.5f}, numerical limit={tangent:.5f}') x = np.arange(0.01, 3, 0.005) plot(x, [f(x), tangent * x + f(1) - tangent * 1], 'x', 'f(x)', legend=['f(x)', 'Tangent line (x=1)'])
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