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Re: Embed extra info?

  • To: mathgroup at
  • Subject: [mg113669] Re: Embed extra info?
  • From: Sam Takoy <sam.takoy at>
  • Date: Sun, 7 Nov 2010 05:10:13 -0500 (EST)
  • References: <iatt2m$egl$> <ib38va$f43$>

On 11/6/2010 6:00 AM, David Bailey wrote:
> On 04/11/10 09:06, Sam Takoy wrote:
>> Hi,
>> I'm writing code that implements tensor calculus. I'm sure it's been
>> done beautifully in MathTensor and other Mathematica packages, but I
>> would like to do it for myself to learn things along the way...
>> Nontensorially speaking, a tensor is a multidimensional array but each
>> dimension is tagged as either upper or lower and certain operations on
>> the array are performed differently depending on the flavor. Is there a
>> way to embed extra info in a List of Lists so that if one does regular
>> things with the List, such as displaying it, the information does not
>> show up, but other operations can extract the extra info and use it?
>> Many thanks in advance!
>> Sam
> The best way to do this, is to wrap the matrix in an extra layer
> together with the other information:
> myTensor[{{1,2},{3,4}},index info, etc....]
> Then overload an operator \[CircleTimes] to represent multiplication
> (you can't use Times because you need a non-commutative operator) and
> overload Times to represent scalar multiplication.
> To improve the appearance of the output, you can add MakeBoxes
> expressions to make myTensor objects display in whatever way you want.
> David Bailey

Thank you very much for your great response!

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