dot products ?s

[pc999]

Can anyone explain me what they are and serve.
I heard thinghs like physics and lightning/shadows, I am right? If so can anyone give me numbers (like how many things "flying around")?

And for last how many of this can Cell (PS3/7spus version) do?


Thanks in advance.

 

[rendezvous]

dot product explained: Dot product at mathoworld

 

[SoVos20]

I have a question about this too.

What do they considure a dot product operation. Example:

The Dotproduct of (1, 3, 4) and (2, 5, 1) would that be 1 dot product operation or would it be 5.

 

[ERP]

That would be 1, 3 part dotproduct operation.

For graphics they usually use 4 vectors so 1 dot porduct is 7 flops

x1*x2+y1*y2+z1*z2+w1*w2

4 multiplies and 3 adds.

But if you wanted to stretch numbers technically

x1*x2+y1*y2

is a dotproduct aswell

 

[SoVos20]

That would be 1, 3 part dotproduct operation.

For graphics they usually use 4 vectors so 1 dot porduct is 7 flops

x1*x2+y1*y2+z1*z2+w1*w2

4 multiplies and 3 adds.

But if you wanted to stretch numbers technically

x1*x2+y1*y2

is a dotproduct aswell

It what about a dot product of R^5+. Like the dot product of (1, 3 ,5 ,6, 5) and (1, 0, 1, 3, 2) would this still be 1 dot product operation and 7 flops.

 

[pc999]

dot product explained: Dot product at mathoworld

Thanks

So if I got it right it serves to calculate directions so it is for physics and lightning/shadows...

This means that if we dedicate a full (xCPU) core for physics we would have 50k (@ 60FPS) thinghs flying around

 

[ERP]

That would be 1, 3 part dotproduct operation.

For graphics they usually use 4 vectors so 1 dot porduct is 7 flops

x1*x2+y1*y2+z1*z2+w1*w2

4 multiplies and 3 adds.

But if you wanted to stretch numbers technically

x1*x2+y1*y2

is a dotproduct aswell

It what about a dot product of R^5+. Like the dot product of (1, 3 ,5 ,6, 5) and (1, 0, 1, 3, 2) would this still be 1 dot product operation and 7 flops.

Yes you can do dotproducts between vectors of any size.

It would require (N+N-1) floating point ops where N is the size of the vector, so a dot product of a 5 vector would be 9 flops.

 

[SoVos20]

That would be 1, 3 part dotproduct operation.

For graphics they usually use 4 vectors so 1 dot porduct is 7 flops

x1*x2+y1*y2+z1*z2+w1*w2

4 multiplies and 3 adds.

But if you wanted to stretch numbers technically

x1*x2+y1*y2

is a dotproduct aswell

It what about a dot product of R^5+. Like the dot product of (1, 3 ,5 ,6, 5) and (1, 0, 1, 3, 2) would this still be 1 dot product operation and 7 flops.

Yes you can do dotproducts between vectors of any size.

It would require (N+N-1) floating point ops where N is the size of the vector, so a dot product of a 5 vector would be 9 flops.

Thanks.

Since M$ said Xbox could do 9 billion Dot Product Operations a second, how many flops would this come out to. 9

 

[Acert93]

Some more links and info in another B3D thread

 

[Shifty Geezer]

Since M$ said Xbox could do 9 billion Dot Product Operations a second, how many flops would this come out to. 9

Depends on what type of DP's they are; how many vectors they work on. As said above, if thats (x,y).(x1,y1), thats 3 flops per dp = 27 Gigaflops. If it's working on 5 vectors, (a,b,c,d,e).(a1,b1,c1,d1,e1), that's 81 Gigaflops.

Like all these metrics, it's useless without details and context.

 

[Titanio]

And for last how many of this can Cell (PS3/7spus version) do?

A crude calculation would be their flops per second divided by 8, for a 4-component vector (since it takes 7 flops) - aka 3.2bn per sec for one SPE. I'd have to let someone else work it out more accurately..

This means that if we dedicate a full (xCPU) core for physics we would have 50k (@ 60FPS) thinghs flying around

? Things flying around? You could have 50m dot products per frame @ 60fps.

 

[pc999]

Thanks titanio.

BTW sotrry the error , not 50k but 50m