Hi David,
> but aside from the fact that the syntax doesn't allow it, if the
> comparison function for two points is not transitive, the answer isn't
> well specified (what does it mean to sort in that case?)
sorry, perhaps I missed your point. My english is not the best.
What do you mean by transitive? Given a set of points the comparison
function of course determines just one possible sorting.
> You only need to do one division don't you? That gives the tangent
> which is enough once you know which quadrant you are in. You don't need
> arctan if you only need to order.
again, perhaps we're talking about different things?! In a set of points I choose
a fix reference point P(0) and sort all the other points P(i) by the increasing counter-clockwise
angle the line segment P(0) - P(i) makes with the x-axis. So the angle is dependent
on the reference point, not the quadrant.
But I think this is far beyond the scope of my thread.
Thanks again for your help!
Claus