Thx Tom!! 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 > 0.999999999999999633651488135693 > > Actually, it's not producing 1, but a smidgen more: > > regression=# set extra_float_digits TO 3; > SET > regression=# select ( cast ( > cos(radians(39.9826557)) > * cos(radians(39.9826557)) > * cos(radians(-0.04773120000004383) - radians(-0.04773120000004383)) > + sin(radians(39.9826557)) > * sin(radians(39.9826557)) as double precision ) > ); > float8 > --------------------- > 1.00000000000000022 > (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 >
