Thread: BUG #4514: Pi division error

The following bug has been logged online:

Bug reference:      4514
Logged by:          Traci Sumpter
Email address:      traci.sumpter@opus.com.au
PostgreSQL version: 8.3.3
Operating system:   Linux
Description:        Pi division error
Details:

I am trying to do some calculations within Postgresql and am not getting the
expected result.  the first set proves that the pi works as expected with
multiplication.

Equation   180*pi
VB         565.486677646163
Calculator 565.486677646163
PostgreSQL 565.486677646163
Php        565.48667764616

However if I extend this equation postgres definately fails this test.

Equation   (315-0)/180*pi
VB         5.49778714378213
Calculator 5.497787144
PostgreSQL 3.14159265358979
Php        5.4977871437821

Help

Traci Sumpter escribió:
> The following bug has been logged online:
>
> Bug reference:      4514
> Logged by:          Traci Sumpter
> Email address:      traci.sumpter@opus.com.au
> PostgreSQL version: 8.3.3
> Operating system:   Linux
> Description:        Pi division error
> Details:
>
> I am trying to do some calculations within Postgresql and am not getting the
> expected result.  the first set proves that the pi works as expected with
> multiplication.
>
> Equation   180*pi
> VB         565.486677646163
> Calculator 565.486677646163
> PostgreSQL 565.486677646163
> Php        565.48667764616
>
> However if I extend this equation postgres definately fails this test.
>
> Equation   (315-0)/180*pi
> VB         5.49778714378213
> Calculator 5.497787144
> PostgreSQL 3.14159265358979
> Php        5.4977871437821
>
> Help
>
>
hola el problema que entero/entero = entero
lo que debes hacer es

(315.0-0)/180*pi


saludos Fernando

On 2008-11-06 07:56, Traci Sumpter wrote:

> Equation   (315-0)/180*pi
> PostgreSQL 3.14159265358979

You equation in SQL looks like this:

=> select (315-0)/180*pi from (select 3.14159265358979 as pi) as a;

Which is an equivalent of:

=> select (315/180)*pi from (select 3.14159265358979 as pi) as a;

And because 315 and 180 are integers so (315/180) is rounded down to
integer (1):

=> select 1*pi from (select 3.14159265358979 as pi) as a;

I think you need:

=> select (315.0-0)/180*pi from (select 3.14159265358979 as pi) as a;
5.497787143782132500000000000000

Any strongly typed language will do this, for example in python:

$ python -c 'pi=3.14159265358979; print (315-0)/180*pi;'
3.14159265359
$ python -c 'pi=3.14159265358979; print (315.0-0)/180*pi;'
5.49778714378

Regards
Tometzky
--
...although Eating Honey was a very good thing to do, there was a
moment just before you began to eat it which was better than when you
were...
                                                      Winnie the Pooh