I am looking at the following formula that defines the vector that contains the diagonal elements of a matrix:

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$v$ is a vector and $A$ is a matrix (rectangular or square).

I understand every symbol used in the formula except the comma indicated by the red arrow.

My best guess is that it is to separate the formula from the definition of the numbers contained in $i$. Is that so?


Yes, that is exactly so. So it's more of a linguistic comma than a mathematically significant one.

  • $\begingroup$ I would read it as "where" if reading out loud. $\endgroup$ – Nick Matteo Dec 14 '19 at 18:32
  • $\begingroup$ @NickMatteo I would say "where" (or maybe "for") even if it weren't there, so I don't think I would read it out loud at all. $\endgroup$ – Arthur Dec 14 '19 at 18:45

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