Re: Any possible optimization?

[Daniel Arteaga]

Al 10/01/11 18:39, En/na CdeMills ha escrit:

> If the function is called many times from the same place, the best way is to
> not use function call at all and vectorise the code. Let say that your
> points coordinates are in row matrices:
> aa = b-a; bb = c-d; cc = c-a;
> my_idet = 1./(aa(:, 1).*bb(:, 2)-aa(:, 2).*bb(:, 1));
> s = (bb(:, 2).*cc(:, 1) - bb(:, 1).*cc(:, 1)).*my_idet;
> t = (aa(:, 1).*cc(:, 2) - aa(:, 2).*cc(:, 1)).*my_idet;
>
> This way, there is no 'for' loop, nor function call.

I cannot vectorize this part of my code since the calculation at a given 
iteration depends on the previous iteration. Any suggestion of how this 
situation can be handled more efficiently is welcome.

To give background, I'm exploring a terrain map composed of triangles, 
and the goal is to obtain a section of the map by intersecting a given 
direction with the vertices of the triangles. The triangle to explore 
depends on the previous segment intersected.

> The names of variables
> should not alias function names (det). The last small optimisation is that
> (I learned it a long time ago), floating point division is slower than
> multiplication, so the inverse of the determinant is computed only once.

I just implemented this, and the performance gains are very modest. 
Interesting to take into account nevertheless.

Thank you very much,

Daniel