import matplotlib.pyplot as plt
import numpy as np
from math import log10

abscisses=np.logspace(0, 2, num=10, base=10) 
ordonnees=[2*log10(3*x) for x in abscisses]

plt.plot(abscisses, ordonnees, 'ro')

plt.xscale('log')
plt.yscale('log')
plt.title("Fonction x -> 2*log10(3*x)")

plt.grid(which="major", axis="x", linewidth=1.5, linestyle='-')
plt.grid(which="major", axis="y", linewidth=1.5, linestyle='-')
plt.grid(which="minor", axis="x", linewidth=0.75, linestyle='-', color='0.75')
plt.grid(which="minor", axis="y", linewidth=0.75, linestyle='-', color='0.75')
plt.show()