Thread Subject: cross product and mat lab

Hey guys I was wondering I have 3 vectors: a, b, c. now
finding the cross product of them on paper is straight
forward but how would mat lab do a x b .c and a.b x c if a =
(1,2,3), b = (4,5,6) and c = (7,8,9)

Thanks!

On 6 Feb, 14:07, "Rufus Worrell" <hollywoodba...@AOL.com> wrote:
> Hey guys I was wondering I have 3 vectors: a, b, c. =A0now
> finding the cross product of them on paper is straight
> forward but how would mat lab do a x b .c and a.b x c if a =3D
> (1,2,3), b =3D (4,5,6) and c =3D (7,8,9)
>
> Thanks!

help cross
help dot

Rune

see help on cross and dot! I hope, you will easily solve your problem, if you think a little deeper.

"Rufus Worrell" <hollywoodbatez@AOL.com> wrote in message
<focbdu$hvp$1@fred.mathworks.com>...
> Hey guys I was wondering I have 3 vectors: a, b, c. now
> finding the cross product of them on paper is straight
> forward but how would mat lab do a x b .c and a.b x c if
a =
> (1,2,3), b = (4,5,6) and c = (7,8,9)
>
> Thanks!

Hi,

dot(cross(a,b),c)

and

dot(a,cross(b,c))


should solve your homework. The result lies between -0.001
and +0.001 :-)


Cheers,

Thomas

"Rufus Worrell" <hollywoodbatez@AOL.com> wrote in message <focbdu$hvp
$1@fred.mathworks.com>...
> Hey guys I was wondering I have 3 vectors: a, b, c. now
> finding the cross product of them on paper is straight
> forward but how would mat lab do a x b .c and a.b x c if a =
> (1,2,3), b = (4,5,6) and c = (7,8,9)
>
> Thanks!
----------
  The quantities

 (a x b) . c
 (b x c) . a
 (c x a) . b
 a . (b x c)
 b . (c x a)
 c . (a x b)

all give the same value and they can all be evaluated as

 det([a;b;c])

  In your particular example the answer will be zero because a, b, and c are
linearly dependent, which is to say that they are coplanar. There is zero
volume in the parallelepiped formed by them.

Roger Stafford