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I'm not sure whether to post this here or on TeX.SE. If it belongs there, please move it.

When working with unit vectors in physics class, we usually write them with an upside down hat, like this: $\check{\imath}\, \check{\jmath} \,\check{\rho}$. But when looking online, I usually found them written like this: $\hat{\imath}\, \hat{\jmath} \,\hat{\rho}$. Is there a correct way to do it, or is it just convention?

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up vote 5 down vote accepted

I have never seen the upside-down hat, but I don't really think it matters so long as you mention it explicitly the first time you use it and you remain consistent afterwards. I'm very used to the upward hat - in my linear algebra classes, that's how I have taught it. And when I dabble in physics, it plays nicely with their concepts of measurables in quantum mechanics.

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