Обсуждение: what do the operator * exactly ?

Does somebody can explain me what the operators * and / do exactly?
for example
select '(1,1)'::point * '(2,2)':: point ;
gives
(0,4)

select '(1,1)'::point * '(3,3)'::point ;
gives
(0,6)

and what does the / operator ?
thanks for your response


MOLINET S.

On Wed, May 29, 2002 at 03:48:22PM +0200, molinet wrote:
> Does somebody can explain me what the operators * and / do exactly?
> for example
> select '(1,1)'::point * '(2,2)':: point ;
> gives
> (0,4)

Well, i imagine it's treating them like complex numbers and multiplying them
giving a rotation/scale conbination.

(1 + 1i) * (2 + 2i) = (0 + 4i)

> select '(1,1)'::point * '(3,3)'::point ;
> gives
> (0,6)

(1 + 1i) * (3 + 3i) = (0 + 6i)

> and what does the / operator ?
> thanks for your response

Does a division probably. It's a bit tricky analytically but if you imagine
that the point (2,2) means to scale by 2*sqrt(2) (the distance from (0,0))
and to rotate by 45 degrees (the angle between the X-axis and the line
joining (0,0) and (2,2)) you're getting there.

HTH,
--
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Canada, Mexico, and Australia form the Axis of Nations That
> Are Actually Quite Nice But Secretly Have Nasty Thoughts About America

> Does somebody can explain me what the operators * and / do exactly?

Scaling and rotation. Addition/subtraction does translation.

> for example
> select '(1,1)'::point * '(2,2)':: point ;
> gives
> (0,4)

This is analogous to complex arithmetic, where there are two orthogonal
dimensions. If you multiply '(1,1)'::point by '(2,0)'::point, then it
appears to be simple scaling. If you multiply by '(0,1)'::point instead,
then it is a rotation, flipping the input about the X axis.

hth

                     - Thomas