posted 10-28- 08:37 AM               

In case you need a cross product algo:

code:

---

	vec.v[x] = a.v[y]*b.v[z] - a.v[z]*b.v[y];
	vec.v[y] = a.v[z]*b.v[x] - a.v[x]*b.v[z];
	vec.v[z]= a.v[x]*b.v[y] - a.v[y]*b.v[x];

---

You will have to normalise the resulting vector, as the magnitude of the resulting cross product represents the area of a imaginary parrelellagram like shape, and is not nessaserily of normal length.

I hope that helps, let me know if you want anything else.

-bryan

posted 10-30- 05:41 PM               

The main drawback for a recursive algorithm is that it requires function calls, which tend to be slow on pretty much every mainstream processor. So if anything, newer processor make a recursive algorithm more appealing, since the processor may be fast enough to make up for the inherent inefficiencies.

Any recursive algorithm can be rewritten as an iterative algorithm. Depending on what you can pre-compute, the iterative version will usually be faster, albeit maybe not as simple and elegant. I once wrote a program to decode fax images. The recursive version took four minutes for a page-sized image. The iterative version took 20 seconds.

posted 10-31- 07:52 PM            

To me, understanding recursion is more difficult that using iteration. But LISP as a language (from what I have seen) is very well suited for using recursion.

If anyone wants to translate this, then go ahead. It tells you if you what variables you have in a list using the syntax (+ 2 3) is the same as 2 + 3. It omits operators and allows or unary "-" as well.

(define (vars f)
(if (pair? f)
(if (pair? (cddr f))
(union (vars (lhs f))
(vars (rhs f)))
(vars (lhs f)))
(if (symbol? f)
(cons f '())
'())))

posted 11-01- 03:31 PM               

I do know that Learn Game Programming in 21 Days was recommended a lot a few years ago. Not all of the 21 Days books were very good, but I heard good things about that one.