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Homework Help: The gradient of a tensor

  1. Jan 7, 2016 #1
    1. The problem statement, all variables and given/known data
    We have the following orthogonal tensor in R3:
    [itex] t_{ij} (x^2) = a (x^2) x_i x_j + b(x^2) \delta _{ij} x^2 + c(x^2) \epsilon_ {ijk} x_k [/itex]
    Calculate the following quantities and simplify your expression as much as possible:
    [itex] \nabla _j t_{ij}(x)[/itex]
    [itex] \epsilon _{ijk} \nabla _i t_{jk}(x) = 0 [/itex]​

    2. Relevant equations
    The equations given in my book are:
    [itex] (\nabla f)_i = \Lambda _{ji} \frac{\partial f}{\partial x_j} [/itex] ( with a tilda on the last xj
    [itex] \nabla _i = \Lambda_i^j \nabla _j [/itex] (with a tilda "~" on the last nabla)
    3. The attempt at a solution
    My problem is that these equations that I have are all assuming that you have a tensor in the form of a matrix, but this is not the case I believe. Also in the book leading up to these equations you have a vector x which is dependent on xi and on ei. Which is now also not the case. Only the first term with a is dependent on xi or xj, but I can't imagine that the rest of the function just falls away..
  2. jcsd
  3. Jan 7, 2016 #2


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    Your notation is unfamiliar.
    What do ##x,x^2## and ##x_i## represent in your formula?
    Does ##t_{ij}(x^2)## represent the ##i,j## component of the tensor, in some assumed (but unstated) basis, calculated in terms of a parameter ##x^2##? Or does it represent the application of an order-2 tensor to a vector denoted by the symbol ##x^2##?
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