loan python實現

import math
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.ticker import MultipleLocator, FormatStrFormatter

def averageCapitalInterest(monthRate, total, monthNum):
    x = total * math.pow(1 + monthRate, monthNum) * monthRate / (math.pow(1 + monthRate, monthNum) - 1)
    debtRest = [0] * (monthNum + 1)
    refundPerMonth = [x] * (monthNum + 1)
    refundInterestPerMonth = [0] * (monthNum + 1)
    refundCapitalPerMonth = [0] * (monthNum + 1)

    debtRest[0] = total
    refundPerMonth[0] = 0
    for monthSeq in range(1, monthNum + 1, 1):
        debtRest[monthSeq] = total * math.pow(1 + monthRate, monthSeq) - x * (math.pow(1 + monthRate, monthSeq) - 1) / monthRate
        refundInterestPerMonth[monthSeq] = debtRest[monthSeq - 1] * monthRate
        refundCapitalPerMonth[monthSeq] = x - refundInterestPerMonth[monthSeq]

    totalInterest = sum(refundInterestPerMonth)
    totalRefund = total + totalInterest
    capitalRest = debtRest

    assert((totalRefund-1<sum(refundPerMonth) and totalRefund+1>sum(refundPerMonth)) == True)

    return [totalRefund, totalInterest, debtRest, capitalRest, refundPerMonth, refundInterestPerMonth, refundCapitalPerMonth]

def averageCapital(monthRate, total, monthNum):
    debtRest = [0] * (monthNum + 1)
    refundPerMonth = [0] * (monthNum + 1)
    refundInterestPerMonth = [0] * (monthNum + 1)
    refundCapitalPerMonth = [total/monthNum] * (monthNum + 1)

    debtRest[0] = total
    refundCapitalPerMonth[0] = 0
    for monthSeq in range(1, monthNum + 1, 1):
        debtRest[monthSeq] = debtRest[monthSeq-1] - refundCapitalPerMonth[monthSeq]
        refundInterestPerMonth[monthSeq] = debtRest[monthSeq-1] * monthRate
        refundPerMonth[monthSeq] = refundCapitalPerMonth[monthSeq] + refundInterestPerMonth[monthSeq]

    totalInterest = sum(refundInterestPerMonth)
    totalRefund = total + totalInterest
    capitalRest = debtRest

    assert((totalRefund-1<sum(refundPerMonth) and totalRefund+1>sum(refundPerMonth)) == True)

    return [totalRefund, totalInterest, debtRest, capitalRest, refundPerMonth, refundInterestPerMonth, refundCapitalPerMonth]


if __name__ == "__main__":
    monthRate = 0.049*0.9/12
    total = 1800000
    monthNum = 12 * 30

    investRate = math.pow(1+0.06,1/12) -1
    # investRate = 0.08/12

    [totalRefund, totalInterest, debtRest, capitalRest, refundPerMonth, refundInterestPerMonth,refundCapitalPerMonth] = averageCapitalInterest(monthRate, total, monthNum)
    [totalRefund1, totalInterest1,debtRest1, capitalRest1, refundPerMonth1, refundInterestPerMonth1, refundCapitalPerMonth1] = averageCapital(monthRate, total, monthNum)
    print("等額本息：總共還款："+str(totalRefund)+" 其中利息："+str(totalInterest))
    print("等額本金：總共還款：" + str(totalRefund1) + " 其中利息：" + str(totalInterest1))
    print("等額本息比等額本金多付利息：" + str(totalRefund -totalRefund1))

    cashDiff = [0]*(monthNum + 1)
    investProfit= [0]*(monthNum + 1)
    for i in range(1, monthNum+1, 1):
        cashDiff[i] = refundPerMonth1[i] - refundPerMonth[i]
    for i in range(1, monthNum, 1):
        investProfit[i] = cashDiff[i] * math.pow(1+investRate,monthNum-i)
    print("等額本息月供比等額本金多出的現金投資收益爲：" + str(sum(investProfit)))
    print("等額本息比等額本金,在還完貸款後：" + str(sum(investProfit)-(totalRefund -totalRefund1)))

    for i in range(1,monthNum+1,1):
        print("第"+str(i) +"月 等額本息：月供："+str(refundPerMonth[i])+" 每月還本金："+str(refundCapitalPerMonth[i])+" 剩餘未還本金："+str(debtRest[i]))
        print("第" + str(i) + "月 等額本金：月供：" + str(refundPerMonth1[i]) + " 每月還本金：" + str(refundCapitalPerMonth1[i]) + " 剩餘未還本金：" + str(debtRest1[i]))


    pic = r"E:\loan.png"
    xmajorLocator = MultipleLocator(6)  # 將x主刻度標籤設置爲20的倍數
    xmajorFormatter = FormatStrFormatter('%d')  # 設置x軸標籤文本的格式
    xminorLocator = MultipleLocator(3)  # 將x軸次刻度標籤設置爲的倍數

    ymajorLocator = MultipleLocator(50000)  # 將y軸主刻度標籤設置爲的倍數
    ymajorFormatter = FormatStrFormatter('%1.1f')  # 設置y軸標籤文本的格式
    yminorLocator = MultipleLocator(25000)  # 將此y軸次刻度標籤設置爲的倍數

    x = np.linspace(0, monthNum, monthNum+1)
    plt.figure(1)
    ax1 = plt.subplot(111)
    plt.plot(x, debtRest, 'r')
    plt.plot(x, debtRest1, 'b')

    # 設置主刻度標籤的位置,標籤文本的格式
    ax1.xaxis.set_major_locator(xmajorLocator)
    ax1.xaxis.set_major_formatter(xmajorFormatter)
    ax1.yaxis.set_major_locator(ymajorLocator)
    ax1.yaxis.set_major_formatter(ymajorFormatter)
    # 顯示次刻度標籤的位置,沒有標籤文本
    ax1.xaxis.set_minor_locator(xminorLocator)
    ax1.yaxis.set_minor_locator(yminorLocator)
    ax1.xaxis.grid(True, which='major')  # x座標軸的網格使用主刻度
    ax1.yaxis.grid(True, which='major')  # y座標軸的網格使用次刻度

    plt.legend(["debtRestCI", "debtRest"], loc=0)
    plt.xlabel("month")
    plt.ylabel("amount")
    plt.xlim(0, monthNum)

    plt.figure(2)
    ax2 = plt.subplot(111)
    plt.plot(x, refundPerMonth, 'r')
    plt.plot(x, refundCapitalPerMonth, 'm')
    plt.plot(x, refundPerMonth1, 'c')
    plt.plot(x, refundCapitalPerMonth1, 'g')

    xmajorLocator = MultipleLocator(6)  # 將x主刻度標籤設置爲20的倍數
    xmajorFormatter = FormatStrFormatter('%d')  # 設置x軸標籤文本的格式
    xminorLocator = MultipleLocator(3)  # 將x軸次刻度標籤設置爲的倍數
    ymajorLocator = MultipleLocator(500)  # 將y軸主刻度標籤設置爲的倍數
    ymajorFormatter = FormatStrFormatter('%1.1f')  # 設置y軸標籤文本的格式
    yminorLocator = MultipleLocator(100)  # 將此y軸次刻度標籤設置爲的倍數

    # 設置主刻度標籤的位置,標籤文本的格式
    ax2.xaxis.set_major_locator(xmajorLocator)
    ax2.xaxis.set_major_formatter(xmajorFormatter)
    ax2.yaxis.set_major_locator(ymajorLocator)
    ax2.yaxis.set_major_formatter(ymajorFormatter)
    # 顯示次刻度標籤的位置,沒有標籤文本
    ax2.xaxis.set_minor_locator(xminorLocator)
    ax2.yaxis.set_minor_locator(yminorLocator)
    ax2.xaxis.grid(True, which='major')  # x座標軸的網格使用主刻度
    ax2.yaxis.grid(True, which='major')  # y座標軸的網格使用次刻度

    plt.legend(["refundPerMonthCI", "refundCapitalPerMonthCI", "refundPerMonth", "refundCapitalPerMonth"], loc = 0)
    plt.xlabel("month")
    plt.ylabel("amount")
    plt.xlim(0, monthNum)

    plt.show()
    plt.close(1)
    plt.close(2)