Mathy CAPTCHA

I was confronted with this CAPTCHA today:


My response to it confirms that, not only am I a human, but I’m one that thinks like a computer. ;-)

This isn’t the first mathy one I’ve had by a long shot, but I think it’s the first time that I put in some proper typesetting effort. In hindsight, I know I should have specified \mathsf for the superscript T, but my LaTeX skills have rusted since a I left academia.

When I see a formula like this, I always wonder what it means. I can only guess that y^T is the transpose of y, but then I’m not used to seeing matrices in lowercase. Could y be some other matrix-like type? It’s possible this is a commonly-known construction that I should be ashamed of not recognising. But then I only scored better than 63% of the population in The Difficult Math Quiz, and I supposedly have a degree in the subject. Incidentally, a lot of that quiz comes down to guessing what formulas mean, or which formulas look plausible, without context of where in math they are used — not unlike my conundrum with this one.

(The reason I’m joining StumbleUpon now is that I’ve had a surge in traffic from it in the last 24 hours. I thought I should have a look at how it works and see why my blog is featuring on it. Not that I’m complaining in the slightest.)

Update. Duh.  y is a vector, and Q is a square matrix.  Now it starts to look more plausible.  Is it part of a Markov chain formula?  I can’t believe I don’t know this stuff.

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