IRR library is only good if the pay period and compound period is in years (Engineering Economy)

问题

http://docs.scipy.org/doc/numpy-1.10.0/reference/generated/numpy.irr.html

The link above works for me only when the pay period and compound period are in years. If they in months or quarters, I don't know how to use it.

You will understand what I am saying, if you have knowledge about IRR, present value, future value, etc.

The answer for IRR(Year) is 298.88% and I am getting 12.22%

The time in column A is in years

EXCEL FILE IMAGE: Excel File image

import xlrd
import numpy

fileWorkspace = 'C://Users/jod/Desktop/'

wb1 = xlrd.open_workbook(fileWorkspace + 'Project3.xls')
sh1 = wb1.sheet_by_index(0)

time,amount,category = [],[],[]
for a in range(2,sh1.nrows):
    time.append(int(sh1.cell(a,0).value))
    amount.append(float(sh1.cell(a,1).value))
    category.append(str(sh1.cell(a,2).value))
#print(time)
#print(amount)
#print(category)
print('\n')

p_p2 = str(sh1.cell(0,1))
p_p1 = p_p2.replace("text:'","")
pp = p_p1.replace("'","")
#print(pp)
c_p2 = str(sh1.cell(1,1))
c_p1 = c_p2.replace("text:'","")
cp = c_p1.replace("'","")
#print(cp)

netflow = 0
outflow = 0
inflow = 0
flow = 0
if pp == "Months" and cp == "Months":

    IRR = numpy.irr(amount) * 100
    print ("IRR:", round(IRR, 2), '%', '\n')

    for i in time: 
        flow = amount[i] / numpy.power((1 + (IRR/100)), time[i])
        if flow>0:                      
            inflow = inflow + flow      
        if flow<0:                      
            outflow = outflow + flow   

        #print ('Present Value (P) is:', round(flow,0), '\n')

    netflow = outflow + inflow
    print("In 2016")
    print("-------")
    print ('Outflow is: ', round(outflow,0))
    print ('Inflow is: ', round(inflow,0))
    print ('Netflow is: ', round(netflow,0), '\n')

    outflow2 = (round(outflow,0))*(1+(IRR/100))**(9)
    inflow2 = (round(inflow,0))*(1+(IRR/100))**(9)
    netflow2 = outflow2 + inflow2

    print("In 2025")
    print("-------")
    print ('Outflow is: ', round(outflow2,0))
    print ('Inflow is: ', round(inflow2,0))
    print ('Netflow is: ', round(netflow2,0), '\n')

回答1:

Let us assume we have a monthly flow, for example:

flow = [-1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1.4]
x = np.irr(flow)
x
0.0284361557263606

to compute IRR you need to use the following formula: IRR = (1 + x)**12 - 1

(1 + x) ** 12 - 1
0.39999999999998925

If you have quarterly flow, use the formula acordingly:

IRR = (1 + np.irr(quarterly_flow)) ** 4 - 1

回答2:

According to numPy link that you provided. It's for periodic IRR, which means, it depends on what is your definition of 'periodic' it could be monthly or annually.

For example, as I followed your provided data:

amount_arr = [-17.99, 7.99, -3.00, 7.99, -3.00, 7.99, -3.00, 7.99, -3.00, 7.99, -3.00, 7.99]

airr = np.irr(amount_arr)

print ('periodic IRR is %2.2f%%' %(100 * airr))
print ('annual is %2.2f%%' %(12 * (100 * airr)))

> periodic IRR is 12.22%
> annual is 146.66%

Hope it helps.

来源：https://stackoverflow.com/questions/35713992/irr-library-is-only-good-if-the-pay-period-and-compound-period-is-in-years-engi

标签

python

excel

numpy

economics

irr