Precision Tail-off?
Peter J. Holzer
hjp-python at hjp.at
Sat Feb 18 06:16:01 EST 2023
On 2023-02-18 03:52:51 +0000, Oscar Benjamin wrote:
> On Sat, 18 Feb 2023 at 01:47, Chris Angelico <rosuav at gmail.com> wrote:
> > On Sat, 18 Feb 2023 at 12:41, Greg Ewing via Python-list
> > > To avoid it you would need to use an algorithm that computes nth
> > > roots directly rather than raising to the power 1/n.
> > >
> >
> > It's somewhat curious that we don't really have that. We have many
> > other inverse operations - addition and subtraction (not just "negate
> > and add"), multiplication and division, log and exp - but we have
> > exponentiation without an arbitrary-root operation. For square roots,
> > that's not a problem, since we can precisely express the concept
> > "raise to the 0.5th power", but for anything else, we have to raise to
> > a fractional power that might be imprecise.
>
> Various libraries can do this. Both SymPy and NumPy have cbrt for cube roots:
Yes, but that's a special case. Chris was talking about arbitrary
(integer) roots. My calculator has a button labelled [x√y], but my
processor doesn't have an equivalent operation. Come to think of it, it
doesn't even have a a y**x operation - just some simpler operations
which can be used to implement it. GCC doesn't inline pow(y, x) on
x86/64 - it just calls the library function.
hp
--
_ | Peter J. Holzer | Story must make more sense than reality.
|_|_) | |
| | | hjp at hjp.at | -- Charles Stross, "Creative writing
__/ | http://www.hjp.at/ | challenge!"
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 833 bytes
Desc: not available
URL: <https://mail.python.org/pipermail/python-list/attachments/20230218/419a6366/attachment.sig>
More information about the Python-list
mailing list