Re: Problem in - Mailing list pgsql-sql

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/

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