Re: Cross Product

Hi Carl,

Are you possibly referring to the Kronecker (tensor) product
(http://en.wikipedia.org/wiki/Kronecker_product)? For two vectors
(length m and n), the Kronecker product gives a matrix (size m x n)
whose elements are all the combinations of products of the components of
the original vectors.

-Travis-

Dennis Shea wrote:
> Carl J. Schreck, III wrote:
>> Is there a built-in way to do a cross product in ncl? For example, if
>> you have an array of length m and another of length n, it would return
>> a matrix that's m x n? I see dot products mentioned in the
>> documentation for matrix multiply (#), but no cross product.
>>
> I guess I don't see exactly what you mean.
> Are not cross products only defined in 3D space?
> I have a cross product function but it is pretty simple.
>
>
> function cross_prod(a[*][3]:numeric, b[*][3]:numeric)
> ; calculate a cross product: c = a x b
> begin
> c = new ( dimsizes(a), typeof(a), "No_FillValue")
>
> c(:,0) = a(:,1)*b(:,2)-a(:,2)*b(:,1)
> c(:,1) = a(:,2)*b(:,0)-a(:,0)*b(:,2)
> c(:,3) = a(:,0)*b(:,1)-a(:,1)*b(:,0)
>
> return(c)
> end
>
>
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-- 
Travis A. O'Brien
Graduate Student Researcher
Earth and Planetary Science Dept.
UC Santa Cruz
tobrien_at_ucsc.edu
(831) 459-3504
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