Yep, I focused on all trigonometric functions take arguments and return
values of type double precision. Looking for the error I lost focus on
numeric values directly on the select and diff inner calculations.
I think best approach will be maintain double precision on trigonometric
calculations for faster and cast to numeric before acos operation.
Thank you man!
2014-02-13 18:26 GMT+01:00 Tom Lane <t...@sss.pgh.pa.us>:
> =?ISO-8859-1?Q?Daniel_V=E1zquez?= <daniel2d2...@gmail.com> writes:
> > Please can someone tell me why this behavior? Thx!!
> You're confusing numeric and double precision; in particular this
> calculation is *not* being done in float8, but numeric:
> > # select (0.766238989559398 * 0.766238989559398 * 1 + 0.642555686986733 *
> > 0.642555686986733) calc;
> > (*) Why this calculation produces 1 and not
> Actually, it's not producing 1, but a smidgen more:
> regression=# set extra_float_digits TO 3;
> regression=# select ( cast (
> * cos(radians(39.9826557))
> * cos(radians(-0.04773120000004383) - radians(-0.04773120000004383))
> + sin(radians(39.9826557))
> * sin(radians(39.9826557)) as double precision )
> (1 row)
> You've got roundoff error either way, but this way happens to be in the
> direction that makes acos() complain.
> regards, tom lane