week 8

视频总结：
视频范围：week1

The recipe for deducing square root cannot be made into a real computer program because computers cannot guess a starting value for y.

answer : True

计算机不能根据经验猜初始值

程序计数器A program counter：
指向程序将执行的下一条命令points the computer to the next instruction to execute in the program.

Determines whether a string is legal：Syntax
Determines whether a string has meaning：Static semantics
Assigns a meaning to a legal sentence：Semantics

十一章总结
解决python3.x版本报错:No module named 'pylab'

conda install numpy
conda install scipy
conda install matplotlib

完整代码：

import pylab
def findPayment(loan, r, m):
    """
    假设loan和r是浮点数， m是整数
    返回一个总额为loan，月利率为r，期限为m个月的抵押贷款的每月还款额
    """
    return loan*((r*(1+r)**m)/((1+r)**m - 1))

class Mortgage(object):
    """建立不同种类抵押贷款的抽象类"""
    def __init__(self, loan, annRate, months):
        self.loan = loan
        self.rate = annRate/12.0
        self.months = months
        self.paid = [0.0]
        self.outstanding = [loan]
        self.payment = findPayment(loan, self.rate, months)
        self.legend = None #description of mortgage

    def makePayment(self):
        self.paid.append(self.payment)
        reduction = self.payment - self.outstanding[-1]*self.rate
        self.outstanding.append(self.outstanding[-1] - reduction)

    def getTotalPaid(self):
        return sum(self.paid)

    def __str__(self):
        return self.legend

    def plotPayments(self, style):
        pylab.plot(self.paid[1:], style, label = self.legend)

    def plotBalance(self, style):
        pylab.plot(self.outstanding, style, label = self.legend)

    def plotTotPd(self, style):
        totPd = [self.paid[0]]
        for i in range(1, len(self.paid)):
            totPd.append(totPd[-1] + self.paid[i])
        pylab.plot(totPd, style, label = self.legend)

    def plotNet(self, style):
        totPd = [self.paid[0]]
        for i in range(1, len(self.paid)):
            totPd.append(totPd[-1] + self.paid[i])
        equityAcquired = pylab.array([self.loan] * len(self.outstanding))
        equityAcquired = equityAcquired - pylab.array(self.outstanding)
        net = pylab.array(totPd) - equityAcquired
        pylab.plot(net, style, label = self.legend)

class Fixed(Mortgage):
    def __init__(self, loan, r, months):
        Mortgage.__init__(self, loan, r, months)
        self.legend = 'Fixed, ' + str(r*100) + '%'

class FixedWithPts(Mortgage):
    def __init__(self, loan, r, months, pts):
        Mortgage.__init__(self, loan, r, months)
        self.pts = pts
        self.paid = [loan*(pts/100.0)]
        self.legend = 'Fixed, ' + str(r*100) + '%, '\
        + str(pts) + ' points'

class TwoRate(Mortgage):
    def __init__(self, loan, r, months, teaserRate, teaserMonths):
        Mortgage.__init__(self, loan, teaserRate, months)
        self.teaserMonths = teaserMonths
        self.teaserRate = teaserRate
        self.nextRate = r/12.0
        self.legend = str(teaserRate*100)\
        + '% for ' + str(self.teaserMonths)\
        + ' months, then ' + str(r*100) + '%'

    def makePayment(self):
        if len(self.paid) == self.teaserMonths + 1:
            self.rate = self.nextRate
            self.payment = findPayment(self.outstanding[-1],self.rate,self.months - self.teaserMonths)
        Mortgage.makePayment(self)

def compareMortgages(amt, years, fixedRate, pts, ptsRate,
    varRate1, varRate2, varMonths):
    totMonths = years*12
    fixed1 = Fixed(amt, fixedRate, totMonths)
    fixed2 = FixedWithPts(amt, ptsRate, totMonths, pts)
    twoRate = TwoRate(amt, varRate2, totMonths, varRate1, varMonths)
    morts = [fixed1, fixed2, twoRate]
    for m in range(totMonths):
        for mort in morts:
            mort.makePayment()
    plotMortgages(morts, amt)

def plotMortgages(morts, amt):
    def labelPlot(figure, title, xLabel, yLabel):
        pylab.figure(figure)
        pylab.title(title)
        pylab.xlabel(xLabel)
        pylab.ylabel(yLabel)
        pylab.legend(loc = 'best')
    styles = ['k-', 'k-.', 'k:']
    #给图编号赋名
    payments, cost, balance, netCost = 0, 1, 2, 3
    for i in range(len(morts)):
        pylab.figure(payments)
        morts[i].plotPayments(styles[i])
        pylab.figure(cost)
        morts[i].plotTotPd(styles[i])
        pylab.figure(balance)
        morts[i].plotBalance(styles[i])
        pylab.figure(netCost)
        morts[i].plotNet(styles[i])
    labelPlot(payments, 'Monthly Payments of $' + str(amt) +
    ' Mortgages', 'Months', 'Monthly Payments')
    labelPlot(cost, 'Cash Outlay of $' + str(amt) +
    'Mortgages', 'Months', 'Total Payments')
    labelPlot(balance, 'Balance Remaining of $' + str(amt) +
    'Mortgages', 'Months', 'Remaining Loan Balance of $')
    labelPlot(netCost, 'Net Cost of $' + str(amt) + ' Mortgages',
    'Months', 'Payments - Equity $')

compareMortgages(amt=200000, years=30, fixedRate=0.07,pts = 3.25, ptsRate=0.05,varRate1=0.045, varRate2=0.095, varMonths=48)