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Is there a notation for a matrix which columns are the same vector?

$$ x = \left[\begin{array}{ccc}x_1 & x_2 & x_3\end{array}\right]^{T} \\ y = \left[\begin{array}{ccc}x & x & x\end{array}\right] $$

Is there a proper notation for $y$?

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  • $\begingroup$ Maybe $[1,1,1]\otimes x$ ? I think maybe it is $\sum_i e_i\otimes x$. I don't have full insight in how the kronecker product relates to the tensor product, but i think both can be see as "vector times vector". $\endgroup$
    – Emil
    Aug 29, 2018 at 7:18
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    $\begingroup$ $Y=x1^T$ is often useful. Here $1$ is a column vector, whose elements are all equal to one. $\endgroup$
    – greg
    Aug 29, 2018 at 18:15

2 Answers 2

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The notation you have for $y$ is fine. It's common block matrix notation.

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Sometimes I've seen it wrote like this $$\left(\begin{matrix} |&|&|\\x&x&x\\|&|&|\end{matrix}\right)$$ The form you suggested doesn't seems right to me, but I could be wrong!

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