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Seeing Tensor Products

  1. Sep 17, 2013 #1
    "Seeing" Tensor Products

    Is there a way to "visualize" the tensor product of two (or ##n##) vectors/tensors/algebras/etc.?

    I'm having a lot of trouble making the tensor product feel intuitive. I know its properties, and I can usually apply it without too much of a problem, but it does not feel "easy." Any ideas?
  2. jcsd
  3. Sep 17, 2013 #2
    For tensor actions in general, I always started by thinking about the properties in lower dimensional spaces, where they can make more physical sense or can be mapped out/drawn explicitly on paper. It tends to bolster your intuition for what happens with higher rank objects.

    Then, you can just think of a general action as something that you can already visualize, but in a projected sense (ie, you are imagining only a part of the true behavior, as more exists "behind the scenes," but it is enough to know what's going on).
  4. Sep 18, 2013 #3
    I'm probably coming at this from a different perspective from you, but maybe this can help. My background is in engineering. I like to visualize that tensor product as a machine for processing vectors. You feed a vector to the machine, and the tensor product maps the vector into a new vector. If [itex]\vec{L}\otimes \vec{R}[/itex] is the vector product of the vectors [itex]\vec{L}[/itex] and [itex]\vec{R}[/itex], then if I dot the vector product on the right by a vector [itex]\vec{V}[/itex], I get:

    [tex](\vec{L}\otimes \vec{R})\centerdot\vec{V}=\vec{L}(\vec{R}\centerdot\vec{V})[/tex]
    This is a vector in the direction of [itex]\vec{L}[/itex], with a magnitude equal to the magnitude of [itex]\vec{L}[/itex] times [itex](\vec{R}\centerdot\vec{V})[/itex]. If I dot the vector product on the left by a vector [itex]\vec{V}[/itex], I get an analogous result.

    As a physicist or mathematician, I don't know if this makes any sense to you. But to me as an engineer it makes perfect sense, and I have used it many time in practice when working with the engineering stress tensor to map a unit normal vector to a surface into the traction vector.

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