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Thread Subject:
dot and cross product of complex numbers with extra values.

Subject: dot and cross product of complex numbers with extra values.

From: Johny Salvo

Date: 13 Dec, 2011 21:09:08

Message: 1 of 2

Hi, I need to find dot and cross products of a two complex number.
I searched matlab help and matlab central, but could not get much about this kind of complex values.
a = 3i + 5j + 7k
b = -2i + 3j –k

so, I wonder that at this point, if I say
dot(a,b) for the doct product and a*b for cross product
dot(a,b) gives 8
a*b gives -8.

I do not now the real value of 'k', but for any value of k, solutions are not change.

I wonder if I am on thr right way, and these results are correct ?

Can anyone help me on this and show any better way of solving this , please.

Subject: dot and cross product of complex numbers with extra values.

From: Roger Stafford

Date: 13 Dec, 2011 23:15:09

Message: 2 of 2

"Johny Salvo" <johnysalvo@yahoo.com> wrote in message <jc8etj$e54$1@newscl01ah.mathworks.com>...
> Hi, I need to find dot and cross products of a two complex number.
> I searched matlab help and matlab central, but could not get much about this kind of complex values.
> a = 3i + 5j + 7k
> b = -2i + 3j –k
>
> so, I wonder that at this point, if I say
> dot(a,b) for the doct product and a*b for cross product
> dot(a,b) gives 8
> a*b gives -8.
>
> I do not now the real value of 'k', but for any value of k, solutions are not change.
>
> I wonder if I am on thr right way, and these results are correct ?
>
> Can anyone help me on this and show any better way of solving this , please.
- - - - - - - - -
  Unless I miss my guess, you are confusing the i used to denote imaginary and complex numbers, with the i, j, k unit orthogonal vectors used in ordinary (Gibbs) three dimensional vector analysis. In the vector analysis sense your vectors a and b have all real components, [3,5,7] and [-2,3,-1] and matlab's 'dot' and 'cross' functions will readily give their dot (scalar) and cross (vector) products. These are not what you show. See:

 http://en.wikipedia.org/wiki/Dot_product
 http://en.wikipedia.org/wiki/Cross_product

  If you are discussing quaternions, the 'dot' and 'cross' products are not the same as quaternion multiplication. Quaternions are an extension of complex numbers into four-dimensinal space. See

 http://en.wikipedia.org/wiki/Quaternion

Roger Stafford

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