On 13.Nov.20.Wed 14:02, Steven D'Aprano wrote:> Hi Kay,
>
> You emailed me off-list, but your email address is bouncing or
invalid,
> so I have no way to email you back.
So THAT's where it went! Sorry about that...yes, it WAS meant
for the group :/!
> [you wrote]
> Okay,but after I import "math" and "decimal",
>
> py> decimal.getcontext().prec=75
> py> print decimal.Decimal(math.atan(1))
> 0.78539816339744827899949086713604629039764404296875
>
> though I set precision to 75, it only did the trig function to
> 50 places AND it is only right to 16 places,
>
> 0.785398163397448309615660845819875721049292349843776...
> (actual).
> [end quote]
>
>
> Here, you calculate the atan of 1 using floating point maths,
> that is, to the precision of C doubles (about 17 decimal
> places). After the calculation is performed using float, you
> then convert it to a Decimal,
> but it is too late, you can't retroactively regain precision.
>
> In a perfect world, this would work:
>
> math.atan(Decimal(1))
>
> but alas, all the functions in the math module convert their
> arguments to float first, so even though your Decimal(1)
> could perform calculations to 75 decimal places, the
> math.atan function downgrades it to a regular float.
Then that is useless! :(
> You could try this third-party module:
>
> http://code.google.com/p/mpmath/
Ah, that looks like just the puppy I'm looking for. :)
Okay then, I just installed the PortableApps version of Python,
but when I downloaded "mpmath-0.17.win32" the installer aborted
with "No Python installation found in the registry".
So I'm trying to install "setuptools 1.4" (and do it that way) at
https://pypi.python.org/pypi/setuptools/1.4
but where is the "Download" link ("Downloads" just shifts down to
the page section)? I'm just looking for the ".zip" file version
(if one exists), not ".tar.gz".
Thx!
--
Kill Hector dead, because Desi sent Milli.
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