# Correct way to typeset a bold and dotted math symbol?

OK, I've seen related questions which indicate that you only bold the main symbol and not subscripts, and a few other almost related questions. But what about when you are using a bold math symbol dotted?

That is, I have a letter which represents a vector. We've been writing vectors as bold letters, i.e \mathbf{u}.

We represent the first time derivative of this symbol by putting a dot on it. Should I bold the dot or not? That is choice:

1. \mathbf{\dot{u}}, or
2. \dot{\mathbf{u}}

Edit: All things equal, I prefer the way choice 2 looks.

• In a general setting, applying some formatting to a symbol (letter, or otherwise) changes its meaning. In a similar way that U is different from \mathcal{U}, say. So, I would keep the operator symbol (\dot in this case) the same and therefore not bold.
– Werner
Apr 29, 2013 at 0:13
• I'd keep option 2. You are differentiating the vector, and thus there is no reason why the dot should be inside the "bolding" command. Apr 29, 2013 at 0:18
• Ah the author forgot \dot inside the \mathbf... would be my reaction to that. Apr 29, 2013 at 0:18
• @percusse huh? reaction to what?
– Jeff
Apr 29, 2013 at 0:24
• Reading a bold dot. Apr 29, 2013 at 0:27

No, you should not print the dot bold. It \dot means a derivative, why should one assume that it's bold version have the same meaning?

• I think you misinterpret what the OP was asking. The bold part of the symbol means it's a vector. What he is asking is whether the dot (meaning the first derivative) should also be bold as well. Apr 29, 2013 at 0:15
• @MarioS.E. It is difficult to give a meaning of (skalar) derivative of a vector, indeed. But if \matxbf{f}=(x^2,0,1) one can interprete its vector derivative as the scalar one. Apr 29, 2013 at 0:25
• @e-birk Thank your for your comment. My answer is earlier than OP's edit. (Corrected, as you had suggested). Apr 29, 2013 at 17:46