# what is the handwritten notation for a random vector?

Not sure if this is a maths question but didn't know where to turn. I'm learning probability theory on my own using a textbook. It uses capital letters with subscripted number to denote random variables (eg, X1,...,Xn) and bold subscripted capital letters (eg, X1,...,Xn) for random vectors. What's the convention for representing the latter in handwritten notes? thanks in advance,

• Maybe $\vec{X_i}$ – anakhro Jul 13 '15 at 16:41
• Putting an arrow above the symbol is the usual convention for handwritten text, but it's really not necessary to use any special notation for vectors versus scalars. – anomaly Jul 13 '15 at 16:42
• In statistics (or mathematics), it is not necessary to make boldface to represent vectors as in physics or engineering. Just put $X$ is fine, if the context is clear. – Zhanxiong Jul 13 '15 at 16:43
• Isn't that exactly what $\mathbb{X}$ is for? – fkraiem Jul 13 '15 at 17:01
• @Zhanxiong: I don't know about engineering, but it's not done in physics (at least at the professional level) either. I don't know whether the arrow is completely unheard of, the way it is in math (see also the $\div$ symbol), but it's definitely not necessary or encouraged. – anomaly Jul 13 '15 at 17:04

## 1 Answer

I teach in my physics class that vectors are shown in textbooks by boldface but are shown in handwriting by adding the vector symbol over the variable. So,

$$\mathbf {X_n}=\overrightarrow {X_n}$$