レッスン5：配列にかける公式

"""Pendulum wave: 24 pendulums making 51, 52, ... 74 swings in 60 seconds.
Run: python pendulum-wave.py   (needs: pip install numpy matplotlib)
"""
import numpy as np
import matplotlib.pyplot as plt

plt.style.use("dark_background")

g, cycle = 9.81, 60.0  # gravity in m/s^2, seconds until they are back in step
n = np.arange(51, 75)  # swings per cycle, one more for each pendulum
period = cycle / n
length = g * (period / (2 * np.pi)) ** 2  # small swings: T = 2 pi sqrt(L / g)
print("lengths in cm:", np.round(length * 100, 1))

fig, axes = plt.subplots(1, 4, figsize=(12, 4), sharey=True)
for ax, t in zip(axes, [0, 15, 20, 30]):
    swing = np.cos(2 * np.pi * t / period)  # where each bob is, from -1 to 1
    ax.scatter(swing, np.arange(len(n)), c=swing, cmap="cool", s=40)
    ax.set_title(f"t = {t} s")
    ax.set_xlim(-1.2, 1.2)
    ax.axis("off")
plt.show()

# Try: t = 60 s (or 75, 80, 90): the same pictures again, as every count is whole