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My paper contains many math expressions like $abcde$ or $abdefv$. Unfortunately, the latter looks very ugly, particularly in regards to the spacing around the f. In particular, there is a significant amount of space around the f which is not present around the other letters.

Is there a method to make that spacing tighter?

Note: Joseph Wright suggested using \! to get a negative thin space. This does seem to help. But I'm still a bit curious as to why the problem occurs at all. For example, it looks fine in $acdfv$ before the f but not after. If anyone has some more details on why the spacing ends up as it does, please comment. Thanks.

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Seems like a very unlikely product - do you really mean this? If so, perhaps try \! to back the spacing up. – Joseph Wright Dec 9 '10 at 17:30
@Joseph Wright: Yes, that's an actual example from my paper, but $efv$ has the same problem and isn't as unlikely. Thanks for the $\!$ advice -- I guess I should have thought about that. That works before the $f$ quite well. Is there a predefined way to get an even thinner negative space (for after the $f$) or should I use $\hspace{-..}$? – A. Rex Dec 9 '10 at 17:38
Sounds like tensor calculus, which leads to, as Spivak calls it in his differential geometry tome, "The debauch of indicies." – Matthew Leingang Dec 9 '10 at 19:44
up vote 18 down vote accepted

For a detailed answer why this is happening you can read this answer of mine (shameless plug indeed): In short, the italic correction of the f has a great part in this. But the italic correction only explains the spacing after the f, not before. For this you have to look at the bounding boxes of the letters:

The first f is a text italic letter in its bounding box, the second one is math italic (in its bounding box together with its italic correction). As you can see, the text letter protrudes a bit to the left (and a lot to the right); the math letter has a tiny bit of white space in the left (and also in the right, because of the italic correction). For a bit more about the bounding boxes see this question of mine (another shameless plug :-)).

I first noticed the problem when typing $Vf$, which doesn't yield a nice output. My resort is using $V\hspace{-0.1em}f$ instead (in a macro, of course), which I like much better. You could even use $V\!f$, but this I find too narrow. Compare these three:


I would not encourage you to follow Caramdir's (now removed) suggestion to use $\mathit{Vf}$ since this uses a different font (text italic, not math italic). You can see quite clearly that the V is narrower (in other words, the angle at the bottom of the V is more acute):

If you use a different math font (like Euler), then the difference is even more noticeable.

(For a case where \textit could be a good solution, see this answer of TH.)

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Thank you for correcting me. I removed my answer. – Caramdir Dec 11 '10 at 18:55
@Caramdir: Thanks for including the bit about the Euler font. – Hendrik Vogt Dec 11 '10 at 21:42
Thank you for a nice answer. Please pardon my two-week absence from this site. – A. Rex Dec 26 '10 at 19:27

Math mode considers each symbol a separate variable, not part of a "word". If you want word-like behaviour, use \mathrm{...} or \mathit{...}. If this really is a product, perhaps using \cdot between factors (or reorganizing, or changing variable names, perhaps distinguished by subindices) helps.

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