What's the correct way to write that a functions is not defined?
e.g.
$$ \begin{bmatrix} a & b & c\\ d & e & f \\ \end{bmatrix} \begin{bmatrix} x\\ y \\ \end{bmatrix} \text{is not defined} $$
or $$ \frac10 \text{is undefined} $$
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That's a matrix and a vector, not a function. I'd typically say something like "The dot (or inner) product is not defined between a matrix and a vector." (Assuming that's what you mean.) – Brian Tung Apr 17 '17 at 21:29
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1The title, on the other hand, makes no use of a centered dot, and that seems to focus attention on whether a matrix product is defined. – hardmath Apr 17 '17 at 21:58
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@hardmath $ \cdot $ gone. I think I should have just written $ \frac10 $ instead. – BanksySan Apr 17 '17 at 22:00
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@BrianTung, Every matrix represents a linear transformation, so calling it a function should be OK. – Chickenmancer Apr 18 '17 at 00:51
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@Justin: I thought of that, but it didn't read like that to me. I'll chalk it up to my misreading it. – Brian Tung Apr 18 '17 at 02:27
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@BrianTung, Nah, I think you read it fine. There's a weird gray area of viewing matrices as arrays and as linear transformations, but both are formally different. – Chickenmancer Apr 18 '17 at 02:31
