On 12/12/07 11:08, Dave Steffen wrote:
On Monday 10 December 2007, Andreas Harnack wrote: [snip]
As far as I'm aware there's only one product to matrices; we're not talking about vectors here ;-). Of course, you can use row- or column-matrices to represent vectors, in which case the result (i.e. scalar or matrix) depends on the order of operands.
You're kidding, right? There are many ways to multiply two matrices together. I listed three above. Cross products are a fourth. The correct interface depends *heavily* on the intended uses.
I also thought outer and cross product dealt with vectors. The following page on outer product: http://documents.wolfram.com/mathematica/Built-inFunctions/AdvancedDocumenta... seems to support that conclusion about outer product, and the following on cross product: http://planetmath.org/encyclopedia/CrossProduct.html also supports that interpretation for cross product. I guess we're both (i.e. me and Andreas) thinking too narrowly. Could you provide some web page supporting your interpretation that outer and cross args are matrices instead of vectors? OOPS, wait. Looking at: http://planetmath.org/encyclopedia/OuterMultiplication.html maybe supports your interpretation, although I can't yet understand all the notation. Anyway, even if I and Andreas are thinking too narrowly, the first two web pages referenced suggest that thinking is understandable and maybe common for those not real familiar with the field. -regards, Larry