horizontal alignment of dot over hat over bold greek letter!

Question

For some strange reason, this:

\hat{\dot{\bm{\phi}}}

prints the dot and the hat slightly off the left of the phi letter. Any ideas if this can be fixed? thanks. Using bm package for bold symbols.

Answer 1

$\mkern4mu\hat{\mkern-4mu\dot{\bm{\phi}}}$

$\skew{3}{\hat}{\skew{3}{\dot}{\bm{\phi}}}$

Answer 2

As to why this happens: TeX handles accents over single characters differently, using the \skewchar of the font. Thus you get nicely aligned math accents only over single characters, and \dot{\bm{\phi}} is already a composed symbol.

If you want double accents, you can use the amsmath or the accents package. However, both packages don't work together well with bm, so the simple \hat{\dot{\bm{\phi}}} won't work with \usepackage{accents}. It took me forever to find out what happens, but here's a fix:

\documentclass{minimal}
\usepackage{bm,accents}

\makeatletter
\newcommand\accbm[1]{\use@mathgroup{\M@OMS}{5}{\bm{#1}}}
\makeatother

\begin{document}
$\hat{\dot{\accbm{\phi}}}$
\end{document}

This gives you . Thus, whenever you want to put accents over \bmed characters, you just have to use \accbm. I should add a few words of caution: 1. It works with \M@OMS, but I don't know if it's the Right Way. 2. In this example, it works with font family 5 in the \use@mathgroup, but I don't know if it'll always work with 5.

UPDATE: Philippe Goutet's great answer to my question How do I identify the encoding and family of a new math font? provides a solution that determines the font family automatically.

Answer 3

It's easier to get accent positioning right if the accents are bold as well as the base. Also if \bm does get confused by its argument adding an extra set of {} stops it trying to disassemble the math construct and instead it sets the entire argumant as a sing;e expression (using \boldmath, essentially) this is a lot simpler (but slower). Note the extra set of braces, and the better accent positioning in row 9.

\documentclass{article}

\usepackage{amsmath}

\usepackage{bm}


\begin{document}

1 $\mathcal{A} \bm{\mathcal{A}}$

2 $\hat{\mathcal{A}} \bm{\hat{\mathcal{A}}}$

3 $\mathcal{\hat{A}} \bm{\mathcal{\hat{A}}}$

4 $\hat{\hat{\mathcal{A}}} \bm{\hat{\hat{\mathcal{A}}}}$

5 $\mathcal{\hat{\hat{A}}} \bm{\mathcal{\hat{\hat{A}}}}$

6 $\phi \bm{\phi}$

7 $\hat{\phi} \bm{\hat{\phi}}$

8 $\hat{\hat{\phi}} \bm{\hat{\hat{\phi}}}$

9 $\hat{\hat{\phi}} \bm{{\hat{\hat{\phi}}}}$

\end{document}