How to put circumflex accent in right position, math mode?

Question

I would like to put a circumflex accent over the letter j when I am in math mode. I was supposed to use $\hat{j}$ but the accent is not exactly over the dot: that is really unpleasant.

What do I have to do to adjust it?

Answer 1

With plain TeX you can use \skew, but the amount of skewing has to be determined case by case. Happily, once the amount has been found it can be made part of a definition.

$\hat{j}$ (normal)

$\skew{4.5}\hat{j}$ (with skew)

\bye

so a definition could be

\def\hatj{\skew{4.5}\hat{j}}

It also works with LaTeX:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

$\hat{j}$ (normal)

$\skew{4.5}\hat{j}$ (with skew)

\end{document}

The output is exactly the same. In this case it's better doing

\newcommand{\hatj}{\skew{4.5}\hat{j}}

Answer 2

If you explicitly need j with dot plus hat then define

\def\hatj{\,\hat{\!j}}

and use \hatj in your document. The reason of this problem is that Knuth did not set the kerning pairs i-skew, j-skew in TeX font metric of cmmi10 font because he probably assumed that these dotted characters will never used with another math accents. The dot-less variants are available.

Note, that "skew" mentioned above is so called "skew character" (charcode 127 in cmmi10). Kerning with skew character controls the horizontal positions of math accents.