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help / color / mirror / Atom feedFrom: Max Lipsky <maxlipsky@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-sql@lists.postgresql.org
Subject: Re: Problem in
Date: Fri, 26 Apr 2019 00:08:27 +0300
Message-ID: <32A34C31-946E-4946-8CD1-DB36F70160ED@gmail.com> (raw)
In-Reply-To: <26108.1556211406@sss.pgh.pa.us>
References: <2164C531-EAA3-4CAF-996F-FEB0E5F73B32@gmail.com>
<26108.1556211406@sss.pgh.pa.us>
Hello Tom!
I think is too much for roundoff error
Found funny post about it:
https://randomascii.wordpress.com/2014/10/09/intel-underestimates-error-bounds-by-1-3-quintillion/ <https://randomascii.wordpress.com/2014/10/09/intel-underestimates-error-bounds-by-1-3-quintillion/;
http://notabs.org/fpuaccuracy/index.htm <http://notabs.org/fpuaccuracy/index.htm;
> On 25 Apr 2019, at 19:56, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Max Lipsky <maxlipsky@gmail.com> writes:
>> SELECT acos(
>> cos(radians(48.9193))
>> * cos(radians(48.9193))
>> * cos(radians(2.5431) - radians(2.5431))
>> + sin(radians(48.9193))
>> * sin(radians(48.9193))
>> ) as result;
>
>> This returned [22003] ERROR: input is out of range
>
> Not too surprising, because (at least on my machine)
>
> regression=# select cos(radians(48.9193))
> regression-# * cos(radians(48.9193)) + sin(radians(48.9193))
> regression-# * sin(radians(48.9193));
> ?column?
> --------------------
> 1.0000000000000002
> (1 row)
>
> Problems of this sort are inevitable when working with finite-precision
> math.
>
> https://en.wikipedia.org/wiki/Round-off_error
>
> regards, tom lane
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Cc: maxlipsky@gmail.com, tgl@sss.pgh.pa.us, pgsql-sql@lists.postgresql.org
Subject: Re: Problem in
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