Re: Why is math.pi slightly wrong?

[Andrew Lee]

Dan Upton wrote:

On Thu, May 22, 2008 at 2:53 PM, Mensanator <mensanator@aol .comwrote:

>On May 22, 11:32 am, "Dutton, Sam" <Sam.Dut...@itn .co.ukwrote:

>>I've noticed that the value of math.pi -- just entering it at the interactive prompt -- is returned as 3.1415926535897 931, whereas (as every pi-obsessive knows) the value is 3.1415926535897 932... (Note the 2 at the end.)
>>>
>>Is this a precision issue, or from the underlying C, or something else? How is math.pi calculated?

>If you actually need that many digits, use a different library.
>>

>>>>import gmpy
>>>>print gmpy.pi(64) # 64 bit precision

>3.141592653589 79323846

>>>>print gmpy.pi(128) # 128 bit precision

>3.141592653589 793238462643383 279502884197

>>>>print gmpy.pi(16384) # 16384 bit precision

>3.141592653589 793238462643383 279502884197169 399375105820974 94459

....

>
Who wants to verify that that's correct to that many digits? ;)

Ramanujan?

http://numbers.computation.free.fr/Constants/Pi/piramanujan.html

[Dutton, Sam]

RE: Why is math.pi slightly wrong?

Thanks for all the answers and comments.

>math.pi is exactly equal to 884279719003555/281474976710656 , which is the closest C double to the actual value of pi

So much for poor old 22/7...

Sam






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[inhahe]

Re: Why is math.pi slightly wrong?

"""
"Dutton, Sam" <Sam.Dutton@itn .co.ukwrote in message
news:mailman.15 01.1211543292.1 2834.python-list@python.org ...
Thanks for all the answers and comments.

>math.pi is exactly equal to 884279719003555/281474976710656 , which is the
>closest C double to the actual value of pi

So much for poor old 22/7...

Sam
"""

The biblically correct version:

import math
math.pi = 3