Question

Hi everyone. I'm doing the second part of Problem Set 1, and I have some code started for how to compute the sum of the logarithms of all the primes from 2 to some number n, but I am stuck at a certain point (see below):

from math import *
n = raw_input('This is a logarithm ratio tester. Which number do you want to test? ')
for x in range(2,n): #picks numbers to test
for divisor in range(2, 1+int(sqrt(x+1))):
if x%divisor == 0: #checks if x is prime
log(x) #computes log of prime

How do I create variable logsum for the sum of all logs for prime values of x?

Answer 1

After I have that variable set up, then I assume I just need to do:

print 'Sum of the logs of the primes is',logsum
print 'n =',n
print 'Ratio of sum to n is',logsum/n

And that will complete the rest of the instructions. Right?

Answer 2

Your beginning and ending points look on point to me. The one thing is though, under your x%divisor is where you what to track your logsum variable. So it should look like:

from math import *
n = raw_input('This is a logarithm ratio tester. Which number do you want to test? ')
*****logsum = 0.0 #Initialize your logsum variable at zero. This will be a float type variable*****
for x in range(2,n): #picks numbers to test
for divisor in range(2, 1+int(sqrt(x+1))):
if x%divisor == 0: #checks if x is prime
**** logsum += log(x) #adds the log of the current prime number to the current sum of all the logs leading up to this point ****

Then you're good to go from there

Answer 3

(Of course, take the asterisks out of the code- I included those just to highlight the parts I added/modified in your original)

Answer 4

That's great help, thanks. I did now wind up with a type error from using a string for the raw_input value, but I corrected it by using

n = int(raw_input('This is a logarithm ratio tester. Which number do you want to test? ')

so now everything is great. Thanks!

Answer 5

Smart people lol