kalenpw - 1 year ago 78

Python Question

I am trying to do the calculation

Using the python decimal module with the following code:

`from decimal import *`

getcontext().prec = 9

sum = Decimal(0)

for i in range(1,11):

sum += Decimal(1/(i**4))

print sum

however, this outputs 1, not a very small fraction like I would expect. I can't find much information here https://docs.python.org/2/library/decimal.html about what is wrong with the code. My guess is sum is not being used as a Decimal in the loop, but I am unsure how to resolve that.

Answer Source

First of all, don't use `sum`

as a variable name, as it is a built-in.

And its sort of necessary to provide at least one float for arithmetic if you expect a float-type answer, here:

```
s = Decimal(0)
for i in range(1,11):
s += Decimal(1./(i**4)) # dividing 1. or 1.0 instead of just 1
print s
```

this gives:

```
1.08203658
```