from matplotlib import pyplot as plt, patches as mpatches

plt.rcParams["figure.figsize"] = [7.50, 3.50]
plt.rcParams["figure.autolayout"] = True

x_tail = 0.1
y_tail = 0.1
x_head = 0.9
y_head = 0.9

fig, ax = plt.subplots()

arrow = mpatches.FancyArrowPatch((x_tail, y_tail), (x_head, y_head), mutation_scale=100, color='green')
ax.add_patch(arrow)

plt.show()