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(Planned finance update - 2022)

# Finance (2nd Edition)
# 2022, 2020 Edward Shore

from math import *

# percent change
def pchg(old,new):
  return (new/old-1)*100

# add sales tax
def taxplus(amt,tax):
  return round(amt*(1+.01*tax),2)

# uniform pv factor pv=pmt*uspv
def uspv(n,i):
  return (1-(1+0.01*i)**(-n))/(0.01*i) 
  
# uniform fv factor fv=pmt*usfv
def usfv(n,i):
  return ((1+0.01*i)**n-1)/(0.01*i)

# monthly payment,(FV = 0, n, I, PV, P/Y=12)
def mopmt(yrs,rate,loan):
  pymt=loan/uspv(yrs*12,rate/12)
  return pymt

# sinking fund,(PV=0, n, I, PMT, P/Y=12)
def sinkfund(yrs,rate,pymt):
  sink=pymt*usfv(yrs*12,rate/12)
  return sink

# piti: principal, interest, taxes, and insurance
def piti(yrs,rate,loan,tax,insur):
  pymt=loan/uspv(yrs*12,rate/12)+(tax+insur)/12
  return pymt

# qualiying income 28:36 ratio
def qualinc(inc,debt,taxins,rate,yrs):
  a=min(inc*0.36-debt,inc*0.28)-taxins
  qual=a*uspv(yrs*12,rate/12)
  return qual

# date number
def datenum(m,d,y):
  if m>2:
    x=int(0.4*m+2.3)
    z=y
  else:
    x=0
    z=y-1
  return 365*y+31*(m-1)+d+int(z/4)-x

# days between dates - actual
def days(m1,d1,y1,m2,d2,y2):
  return datenum(m2,d2,y2)-datenum(m1,d1,y1)

# simple interest
def simpint(p,r,t):
 return p*r/100*t

# total: simple interest
def simptot(p,r,t):
 return p+simpint(p,r,t)

# principal: simple interest
def simpprin(i,r,t):
 return i/(r/100*t)

# Cost-Sell-Margin
# cost 
def cost(sell,margin):
 return sell*(1-margin/100)

# sell
def sell(cost,margin):
 return cost/(1-margin/100)

# margin
def margin(cost,sell):
 return (1-cost/sell)*100

# PV of a single cash stream
def sppv(n,i,fv):
  return fv*(1+i/100)**(-n)

# FV of a single cash stream
def spfv(n,i,pv):
  return pv*(1+i/100)**n

# n of a single cash stream
def spn(i,pv,fv):
  return log(fv/pv)/log(1+i/100)

# i of a single cash stream
def spi(n,pv,fv):
  return ((fv/pv)**(1/n)-1)*100

# net present value - constant period
def npv(flows,rate):
  t=0
  for k in range(len(flows)):
    f=flows[k]
    t+=sppv(k,rate,f)
  return t

# net present value - different periods (days)
def xnpv(flows,dates,rate):
  t=0
  for k in range(len(flows)):
    d=dates[k]/365
    f=flows[k]
    t+=sppv(d,rate,f)
  return t

# internal rate of return - constant period
def irr(flows):
  it=1
  w0=10
  w1=1
  while abs(w1)>1e-12:
    f0=npv(flows,w0)
    f1=npv(flows,w0+.01)
    d=(f1-f0)/.01
    w1=f0/d
    w0-=w1
    it+=1
    if it==201:
      print('Iterations exceeded')
      break
  return w0

# internal rate of return - different periods (days)
def xirr(flows,dates):
  it=1
  w0=10
  w1=1
  while abs(w1)>1e-12:
    f0=xnpv(flows,dates,w0)
    f1=xnpv(flows,dates,w0+.01)
    d=(f1-f0)/.01
    w1=f0/d
    w0-=w1
    it+=1
    if it==201:
      print('Iterations exceeded')
      break
  return w0

# percent of total of a list of values
def ptot(flows):
  s=sum(flows)
  for k in range(len(flows)):
    flows[k]/=s
  return flows

# proroate a value over a list of values
def prorate(flows,amt):
  s=sum(flows)
  for k in range(len(flows)):
    flows[k]/=s
    flows[k]*=amt
  return flows
 
# time value of money - cash flow convetions are followed
# end mode implied, periodic
# payment
def payment(n,i,pv,fv):
  return (-pv-sppv(n,i,fv))/uspv(n,i)

# present value
def present(n,i,pymt,fv):
  return -(pymt*uspv(n,i)+sppv(n,i,fv))

# future value
def future(n,i,pv,pymt):
  return (-pv-pymt*uspv(n,i))*(1+.01*i)**n

# interest
def interest(n,pv,pymt,fv):
  it=1
  w0=10
  w1=1
  while abs(w1)>1e-12:
    f0=pymt*uspv(n,w0)+sppv(n,w0,fv)+pv
    f1=pymt*uspv(n,w0+.01)+sppv(n,w0+.01,fv)+pv
    d=(f1-f0)/.01
    w1=f0/d
    w0-=w1
    it+=1
    if it==201:
      print("Iterations Exceeded")
      break
  return w0

# number of payments
def npmts(i,pv,pymt,fv):
  b=fv-pymt/(.01*i)
  a=-pv-pymt/(.01*i)
  return log(b/a)/log(1+.01*i)