Finding a sum of series in Python 2.7.x

Question

Here's the equation

x + x^2/2 + x^3/3 +.... x^n/n

How will I find the sum of this series? x is a constant term to be entered by user and n which is power is also based on user!

I made this program but it's not working properly.. Have a look -

n=input("Enter power ")
x=input("Enter value of x")
i=0
while i<n:
    c=n-1
    res=(x**(n-c))/(n-(c))
    print res
    i=i+1

So how do we make it? Thanks a ton for your help!

Update : The answers helped me and now the program is working as it should! This was my first time using Stackoverflow! Thanks to everyone for this.

`(n-c)` when `c = n-1` is, upon substitution, same as: `n - (n - 1)` — UltraInstinct, Aug 25 '16 at 17:42
You're calculating the same term over and over again because c and n are never changed in the loop. — Jim Lewis, Aug 25 '16 at 17:42
You are not using `i` in your loop. Also, you should use `for i in range(n)` instead of a `while` loop. — kjaquier, Aug 25 '16 at 17:42

perfect5th · Accepted Answer · 2016-08-25T17:56:51.993

2

Something like this for your loop? Tried to keep it simple.

n = input("Enter power ")
x = float(input("Enter value of x"))

ans = 0
for i in range(1, n+1):
    ans += x**i/i

print(ans)

See zev's answer regarding floats

edited Aug 25 '16 at 17:56

answered Aug 25 '16 at 17:42

perfect5th

score 2 · Answer 2 · edited May 23 '17 at 11:51

2

You're not adding the terms together.

Also, you need to be careful that you use float division when x is an integer. See this thread.

Here's a working implementation:

n = input("Enter power: ")
x = input("Enter value of x: ")
result = 0
for i in range(1, n+1):
    result += (x**i) / float(i)
print result

edited May 23 '17 at 11:51

Community

answered Aug 25 '16 at 17:44

Zev Chonoles

3

@kjaquier: The question does specifically say python 2.7.x – Zev Chonoles Aug 25 '16 at 17:46
Thankyouu! It helped me clear my conceptual thinking on this. Thanks again! :) – Ins Aug 25 '16 at 18:28

score 0 · Answer 3 · answered Aug 25 '16 at 17:59

0

Issue with your program is that your are not adding the sum. See: res=(x**(n-c))/(n-(c)). Instead do:

res += (x**(n-c))/(n-(c))

You may also achieve it by using in-built sum, map and lambda functions as:

y = 5  # or any of your number
sum(map(lambda x: (y**x)/float(x), xrange(1, y)))

answered Aug 25 '16 at 17:59

Moinuddin Quadri

1

Thanks for your efforts! This seems really nice but I am not supposed to use the built in functions! :/ Btw Still Thanks a ton for your efforts! – Ins Aug 25 '16 at 18:29

3 Answers3