# Latex vector notation.

by IlyaZ
Tags: latex, notation, vector
 P: 17 1. The problem statement, all variables and given/known data a. How do I write vectors bold within displaymath and frac. I want Phi, r and r_1 bold. But get G M_1 bold as well = bad. b. How do I use arrows instead of the bold notation? 3. The attempt at a solution \begin{displaymath} a1. textbf{\Phi(r)} = -\frac{G M_1}{| textbf{r}-textbf{r_1} |} \end{displaymath} a2. \bf{\Phi}(\bf{r}) = -\frac{G M_1}{| \bf{r}-\bf{r_1} |}
 P: 321 Arrows: \vec : $$\vec \Phi ( \vec r) = -\frac{G M_1}{| \vec{r}-\vec r_1 |}$$ Bold: \mathbf : $$\mathbf{\Phi}( \mathbf{r}) = -\frac{G M_1}{| \mathbf{r}-\mathbf{r_1} |}$$ I don't think you really want the potential to be a vector, but that's what your code implied, so I kept it.
Mentor
P: 15,157
 Quote by IlyaZ a. How do I write vectors bold within displaymath and frac. I want Phi, r and r_1 bold. But get G M_1 bold as well = bad.
You get other bad stuff as well using \textbf. Don't use it in math mode.

\textbf{\Phi(r)} = -\frac{G M_1}{| \textbf{r}-\textbf{r_1} |}
$$\textbf{\Phi(r)} = -\frac{G M_1}{| \textbf{r}-\textbf{r_1} |}$$

\bf doesn't work at all:
\bf{\Phi}(\bf{r}) = -\frac{G M_1}{| \bf{r}-\bf{r_1} |}
$$\bf{\Phi}(\bf{r}) = -\frac{G M_1}{| \bf{r}-\bf{r_1} |}$$

Timo suggested \mathbf, but that doesn't work on some things.
If you have access to the AMSLaTeX macros, (and you should), use \boldsymbol.

\boldsymbol{\Phi}(\boldsymbol{r}) = -\frac{G M_1}{| \boldsymbol{r}-\boldsymbol{r}_1 |}
$$\boldsymbol{\Phi}(\boldsymbol{r}) = -\frac{G M_1}{| \boldsymbol{r}-\boldsymbol{r}_1 |}$$

 b. How do I use arrows instead of the bold notation?
Use \vec.

An even better solution is to define your own vector macro that formats vectors the way you want them to appear. For example,
\newcommand{\vect}[1]{\boldsymbol{#1}}
Then when someone tells you to format your vectors with arrows instead you can simply change that one macro.
\newcommand{\vect}[1]{\vec{#1}}
Bold symbols are used for things other than vectors (matrices, for example). A global search-and-replace is not a good idea.

 P: 17 Latex vector notation. Thanks, that works great!

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