#!/usr/bin/env python3
import sys

import matplotlib.pyplot as plt
import pandas as pd


def main():
    src = sys.argv[1] if len(sys.argv) > 1 else sys.stdin
    df = pd.read_csv(src)

    fig, ax = plt.subplots(figsize=(10, 5))
    ax.plot(df["time"], df["tao"], label="Tao (symplectic)", linewidth=1)
    ax.plot(df["time"], df["rk4"], label="RK4", linewidth=1)

    ax.set_xlabel("Time")
    ax.set_ylabel("Energy")
    ax.set_title("Double pendulum energy: RK4 vs Tao's method")
    ax.legend()
    ax.grid(True, alpha=0.3)

    fig.tight_layout()
    plt.show()


if __name__ == "__main__":
    main()