# Dotless i and j

1. Nov 16, 2011

### cepheid

Staff Emeritus
I'm wondering how to get dotless i and j in LaTeX on the forums. For some reason, \i and \j don't work for this. I can use \imath and \jmath, and I can even get carets on them to represent unit vectors:

$$\hat{\imath}, \hat{\jmath}$$

The only remaining problem is that I can't get them to be typeset in boldface and upright as vectors traditionally are. If I do this hack:

$$\hat{\textbf{\imath}}, \hat{\textbf{\jmath}}$$

then I can get them boldface, but still not upright. I think that the glyphs for \imath and \jmath are inherently italicized and there is no way to change this. Any suggestions for the OCD among us?

2. Nov 16, 2011

### robphy

From
MathJax can use unicode...

$$\mbox{abcdefgh}\ \unicode{x0131}\unicode{x0237}\ \mbox{klmnopqrstuvwyz}$$

You could define a macro for \i and \j
$\def\i{\unicode{x0131}} \i$ $\def\j{\unicode{x0237}} \j$ (right-click show source)

then use it later
$$\i i\mbox{i}$$ $$\j j\mbox{j}$$

3. Nov 16, 2011

### cepheid

Staff Emeritus
So, definitions that people make using \def are universal and permanent (or at least persist until some user gives the same macro a different definition)???

In any case, it still doesn't work:

$$\def\i{\unicode{x0131}} \hat{\mathbf{\i}}$$

4. Nov 16, 2011

### robphy

How's this?

$\def\ihat{\hat{\unicode{x0131}\!\!\unicode{x0131}}} \ihat$ $\def\jhat{\hat{\unicode{x0237}\!\!\!\unicode{x0237}}} \jhat$

$$8\ihat + 6\jhat$$

I suspect your \defs are local to your post.

5. Nov 16, 2011

### cepheid

Staff Emeritus
That's very interesting! I just read that \! inserts a small negative space. So you have two unicode dotless i's slightly overlapping each other to produce a thicker one. It's very clever. Why the extra space for the j? Why not:

$\def\jhat{\hat{\unicode{x0237}\!\!\unicode{x0237}}} \jhat$

Ah. That's why. A line thickness problem.