import matplotlib.pyplot as plt # 定義された条件 annual_growth_rate_ac = 0.05-0.0015 annual_growth_rate_vt = 0.05-0.0007 dividend_rate = 0.02 initial_investment = 10**7 investment_period = 20 us_tax_rate = 0.1 jp_tax_rate = 0.2 # 資産推移を保持するリスト nisa_account_final = [initial_investment] non_nisa_account_final = [0] regular_growth = [initial_investment] # シミュレーション for year in range(1, investment_period + 1): dividend_nisa = nisa_account_final[-1] * dividend_rate * (1 - us_tax_rate) nisa_growth = nisa_account_final[-1] * (1 + annual_growth_rate_vt - dividend_rate) nisa_account_final.append(nisa_growth) dividend_non_nisa = non_nisa_account_final[-1] * dividend_rate # 米国税を差し引く dividend_non_nisa_after_tax = dividend_non_nisa * (1 - us_tax_rate) * (1 - jp_tax_rate) # 税額控除のために米国勢を計算しておく us_tax = dividend_non_nisa * us_tax_rate # 米国税を差し引いた後の配当を加算 non_nisa_growth = non_nisa_account_final[-1] * (1 + annual_growth_rate_vt - dividend_rate) + dividend_non_nisa_after_tax + dividend_nisa + us_tax non_nisa_account_final.append(non_nisa_growth) regular_growth.append(regular_growth[-1] * (1 + annual_growth_rate_ac)) # 相対誤差の計算 relative_error = [(n + nn - rg) / rg * 100 for n, nn, rg in zip(nisa_account_final, non_nisa_account_final, regular_growth)] # グラフの描画 fig, (ax1, ax2) = plt.subplots(2, 1, figsize=(10, 10)) ax1.plot(nisa_account_final, label="NISA Account (Final)") ax1.plot([n + nn for n, nn in zip(nisa_account_final, non_nisa_account_final)], label="NISA + Non-NISA Account (Final)") ax1.plot(regular_growth, label="Regular Growth (5%)") ax1.set_ylabel("Amount (JPY)") ax1.set_title("Investment Simulation Over 20 Years (Final Corrected)") ax1.legend() ax1.grid(True) ax2.plot(relative_error, label="Relative Error (NISA + Non-NISA vs Regular Growth)", color="red") ax2.set_xlabel("Year") ax2.set_ylabel("Relative Error (%)") ax2.set_title("Relative Error Between NISA + Non-NISA and Regular Growth") ax2.legend() ax2.grid(True) plt.tight_layout() plt.show()