Brecht

Just a quick question to all the mathbuffs out there...

I want to get the crossproduct of 2 vectors, and for this I set up 2 

matrices going into jit.expr with the following expression :

expr "(in[1].p[2]*in[2].p[3])-(in[1].p[3]*in[2].p[2])" "(in[1].p[3]*in 

[2].p[1])-(in[1].p[1]-in[2].p[3])" "(in[1].p[1]*in[2].p[2])-(in[1].p 

I was wondering if this is correct, and maybe if there's a much more 

I want to get the crossproduct of 2 vectors, and for this I set up 2  
matrices going into jit.expr with the following expression :

expr "(in[1].p[2]*in[2].p[3])-(in[1].p[3]*in[2].p[2])" "(in[1].p[3]*in 
[2].p[1])-(in[1].p[1]-in[2].p[3])" "(in[1].p[1]*in[2].p[2])-(in[1].p 
[2]*in[1].p[3])"

I was wondering if this is correct, and maybe if there's a much more  
simple expression or object for this...?

Just a quick question to all the mathbuffs out there...
I want to get the crossproduct of 2 vectors, and for this I set up 2  
matrices goin

crossproduct

I'm not sure but maybe a shader can help. Parts of the shaders derivatives

It's only an idea. Maybe a bit more complicated. But matrices calculations

> Just a quick question to all the mathbuffs out there...

> I want to get the crossproduct of 2 vectors, and for this I set up 2

> matrices going into jit.expr with the following expression :

> expr "(in[1].p[2]*in[2].p[3])-(in[1].p[3]*in[2].p[2])"

> "(in[1].p[3]*in[2].p[1])-(in[1].p[1]-in[2].p[3])"

> "(in[1].p[1]*in[2].p[2])-(in[1].p[2]*in[1].p[3])"

> I was wondering if this is correct, and maybe if there's a much more

> simple expression or object for this...?

I'm not sure but maybe a shader can help. Parts of the shaders derivatives
are don with matrix calculations.
It's only an idea. Maybe a bit more complicated. But matrices calculations
are much faster on gpu than on cpu.

2007/9/27, Brecht Debackere :
>
> Just a quick question to all the mathbuffs out there...
> I want to get the crossproduct of 2 vectors, and for this I set up 2
> matrices going into jit.expr with the following expression :
>
> expr "(in[1].p[2]*in[2].p[3])-(in[1].p[3]*in[2].p[2])"
> "(in[1].p[3]*in[2].p[1])-(in[1].p[1]-in[2].p[3])"
> "(in[1].p[1]*in[2].p[2])-(in[1].p[2]*in[1].p[3])"
>
> I was wondering if this is correct, and maybe if there's a much more
> simple expression or object for this...?
>
> grtz.
> Brecht Debackere
>
> www.autofasurer.net
> M+32(0)498319302
> F+32(0)70429559
> Skype : Bdebackere
> brecht@visualantics.net
>
>
>
>
>
>

The idea is to create quad_strip ribbon my filling up a matrix, with 

the width of the ribbon being calculated using the crossproduct using 

previous position - the position before that

and then calculating the crossproduct of those 2 vectors, normalizing 

it, and then some stuff with adding the current position to the 

crossproduct and using that value for the even vertices of the 

quad_strip. (I think it sounds clearer in my head, but it is for 

http://www.youtube.com/watch?v=fM1qj_OFY4w

On 27 Sep 2007, at 12:56, Ranja Achbar wrote:

> I'm not sure but maybe a shader can help. Parts of the shaders 

> derivatives are don with matrix calculations.

> It's only an idea. Maybe a bit more complicated. But matrices 

> calculations are much faster on gpu than on cpu.

> I want to get the crossproduct of 2 vectors, and for this I set up 

> 2 matrices going into jit.expr with the following expression :

> expr "(in[1].p[2]*in[2].p[3])-(in[1].p[3]*in[2].p[2])" "(in[1].p[3] 

> *in[2].p[1])-(in[1].p[1]-in[2].p[3])" "(in[1].p[1]*in[2].p[2])-(in 

> I was wondering if this is correct, and maybe if there's a much 

> more simple expression or object for this...?

The idea is to create quad_strip ribbon my filling up a matrix, with  
the width of the ribbon being calculated using the crossproduct using  
previous positions :

vector 1 being :
current position - previous position

vector 2 :
previous position - the position before that

and then calculating the crossproduct of those 2 vectors, normalizing  
it, and then some stuff with adding the current position to the  
crossproduct and using that value for the even vertices of the  
quad_strip. (I think it sounds clearer in my head, but it is for  
doing something like this : http://www.youtube.com/watch?v=fM1qj_OFY4w )

> Hi Brecht,
>
> I'm not sure but maybe a shader can help. Parts of the shaders  
> derivatives are don with matrix calculations.
> It's only an idea. Maybe a bit more complicated. But matrices  
> calculations are much faster on gpu than on cpu.
>
> grr.
> Ranja
>
> 2007/9/27, Brecht Debackere :
> Just a quick question to all the mathbuffs out there...
>
> I want to get the crossproduct of 2 vectors, and for this I set up  
> 2 matrices going into jit.expr with the following expression :
>
> expr "(in[1].p[2]*in[2].p[3])-(in[1].p[3]*in[2].p[2])" "(in[1].p[3] 
> *in[2].p[1])-(in[1].p[1]-in[2].p[3])" "(in[1].p[1]*in[2].p[2])-(in 
> [1].p[2]*in[1].p[3])"
>
> I was wondering if this is correct, and maybe if there's a much  
> more simple expression or object for this...?
>
> grtz.


Xray.jit.crossproduct maybe can help you.

Xray.jit.crossproduct maybe can help you.
www.mat.ucsb.edu/~whsmith/


wonderfull. this does exatly what I want, and normalizes as well :)

> Xray.jit.crossproduct maybe can help you.

wonderfull. this does exatly what I want, and normalizes as well :)
thx.

>
> Xray.jit.crossproduct maybe can help you.
> www.mat.ucsb.edu/~whsmith/
> --
> jaz