       Re: Outer product in mathematica

• To: mathgroup at smc.vnet.net
• Subject: [mg51282] Re: [mg51261] Outer product in mathematica
• From: Matteo Delfino <delfino at studenti.ph.unito.it>
• Date: Tue, 12 Oct 2004 01:57:45 -0400 (EDT)
• References: <200410110525.BAA05003@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Jonas Sourlier ha scritto:
> Hi there
>
> In the lections at my University I have learnt that the outer product
> of two Vectors is defined as follows:
>
> (a)       x (b)       = 0
> (a, b)    x (c, d)    = ad - bc
> (a, b, c) x (d, e, f) = (bf - ce, cd - af, ae - bd)
>
> For two four-dimensional Vectors the outer product produces a
> six-dimensional Vector (handled as a skew-symmetric 4x4-matrix).
> The general, axiomatic definition of the outer product says that it is
>
> graduately anti-commutative: u x v = (-1)^(k+l) (v x u)
> bilinear: (u + v) x w = u x w + v x w
>
> for two vectors u, v and w with dimensions k, l, m.
>
>
> Now, my question: The outer product seems to be implemented in
> Mathematica with the function Outer. But whatever I've tried so far
> with Outer I didn't manage to get the outer product of two vectors as
> described above.
>
> Outer[Times, {a,b,c},{d,e,f}]    produces the 3x3-Matrix
>
> {{a d, a e, a f}, {b d, b e, b f}, {c d, c e, c f}}
>
> How can I calculate the outer product of two vectors with Mathematica?
>
> Thank a lot for helping me!
> Jonas
Outer product (or tensor product) and cross product are not the same
thing.Outer product is defined between two tensors and produces a tesor
of higher rank,cross product takes two vector (read:tensor of the same
rank) and produces another vector (read:tensor of the same rank as
before).In mathematica cross product is defined as Cross[] and Outer
product as Outer[].

YOU MUST USE CROSS[].

DEFINITION OF CROSS PRODUCT BY OUTER PRODUCT

It is still possible to extend the definition of Cross[] product to
tensors of any rank,try searching google for informations such as:

http://www.math.wisc.edu/~milewski/321f04/fwnotestensors.pdf