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Integral as the area under a curveΒΆ

Although this is a simple example, it demonstrates some important tweaks:

  • A simple line plot with custom color and line width.
  • A shaded region created using a Polygon patch.
  • A text label with mathtext rendering.
  • figtext calls to label the x- and y-axes.
  • Use of axis spines to hide the top and right spines.
  • Custom tick placement and labels.
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.patches import Polygon

def func(x):
    return (x - 3) * (x - 5) * (x - 7) + 85

a, b = 2, 9  # integral limits
x = np.linspace(0, 10)
y = func(x)

fig, ax = plt.subplots()
plt.plot(x, y, 'r', linewidth=2)

# Make the shaded region
ix = np.linspace(a, b)
iy = func(ix)
verts = [(a, 0)] + list(zip(ix, iy)) + [(b, 0)]
poly = Polygon(verts, facecolor='0.9', edgecolor='0.5')

plt.text(0.5 * (a + b), 30, r"$\int_a^b f(x)\mathrm{d}x$",
         horizontalalignment='center', fontsize=20)

plt.figtext(0.9, 0.05, '$x$')
plt.figtext(0.1, 0.9, '$y$')


ax.set_xticks((a, b))
ax.set_xticklabels(('$a$', '$b$'))

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