[Tex/LaTex] Spacing around longer function argument’s parentheses

math-modespacing

The line

i(x,y,z,t) = \delta(x-\ell_x(z)) \delta(y-\ell_y(z)) \hat{\imath}(\xi(z),t)

enter image description here

produces (for my eyes, at least) too little space between the successive function calls. It is difficult to visually distinguish the three calls. I guess the underlying reason is that the expressions that serve as function arguments are relatively long. For comparison,

i(x,y,z,t) = \delta(x) \delta(y) \hat{\imath}(\xi(z),t)

enter image description here

already looks a lot better in my opinion.

I know that I could

Manually adjust spacing using \, etc., including the option to define a macro that does this automatically.
Insert \cdot as a means of adding seperating space.

However, my question is: Is there a canonical way (e.g. a package) of dealing with this problem? I imagine I'm not the first one to encounter this problem… still, I wasn't able to find useful, general solutions to the problem.

A possible solution might be something along the lines of

i(x,y,t) = \delta \funcargs{x-\ell_x(z)} \delta \funcargs{y-\ell_y(z)} \hat{\imath} \funcargs{\xi(z)}{t}

Note that I find the use of \cdot to be unsatisfying since it introduces inconsistency in the document (sometimes having the dot and sometimes not, with the meaning being the same).

Best Answer

First, let me give a paraphrasing from The TeXbook showing the amounts of spaces between different types of math atoms:

enter image description here

where

Ord includes things like a, \theta, and things inside \mathord or just plain {}'s;
Op includes things like \sin, \gcd, and things inside \mathop;
Bin includes things like \pm, \otimes, and things inside \mathbin;
Rel includes things like \leq, \mid, and things inside \mathrel;
Open includes things like \langle, (, and things inside \mathopen;
Close includes things like \rangle, ), and things inside \mathclose;
Punct includes things like ,, ., and things inside \mathpunct;
Inner includes things like \cdots and things inside \mathinner.

Here is an example plain-tex document illustrating a couple of different ways:

\let\funarg\mathinner
\def\funop#1{\mathop{{}#1}}
$$ i(x,y,z,t) = \delta(x-\ell_x(z)) \delta(y-\ell_y(z)) \hat\imath(\xi(z),t), $$
$$ i\funarg{x,y,z,t} = \delta\funarg{(x-\ell_x(z))} \delta\funarg{(y-\ell_y(z))} \hat\imath\funarg{(\xi(z),t)}, $$
$$ \funarg{i(x,y,z,t)} = \funarg{\delta(x-\ell_x(z))} \funarg{\delta(y-\ell_y(z))} \funarg{\hat\imath(\xi(z),t)}, $$
$$ \funop i(x,y,z,t) = \funop\delta(x-\ell_x(z)) \funop\delta(y-\ell_y(z)) \funop{\hat\imath}(\xi(z),t), $$
\bye

enter image description here

So as you can see, you probably want the last option of using a \mathop atom for the function "name".

With LaTeX, this could be defined as follows (the second row below shows the output of your original code):

\documentclass{article}
\newcommand\funop[1]{\mathop{{}#1}}
\begin{document}
$i(x,y,z,t) = \funop\delta(x-\ell_x(z)) \funop\delta(y-\ell_y(z)) \funop{\hat\imath}(\xi(z),t)$

vs.

$i(x,y,z,t) = \delta(x-\ell_x(z)) \delta(y-\ell_y(z)) \hat{\imath}(\xi(z),t)$
\end{document}

(The reason I didn't include the parenthesis in the command is that I felt it would be too much effort to measure the arguments to decide on the size of the fences. I think it's simpler to just manually define the height with \bigl( etc., and also it's nicer to see the parens in the manuscript instead of {}'s)

enter image description here

Related Solutions

[Tex/LaTex] Ugly spacing around f in math mode

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.)

[Tex/LaTex] Spacing around \text{} in mathmode

It's not the default behavior because you don't always want space. For instance, in your example, you don't want space before \text{If}, since that would indent your equation. Or consider

\[ x = \begin{cases}
         1 & \text{if $f(x)$}
         0 & \text{otherwise}
       \end{cases} \]

Again, that shouldn't be spaced out. Also, like in Caramdir's answer, I re-entered math mode within the \text, which often solves the spacing problems as well. You could define an \stext command for spaced out text:

\newcommand*{\stext}[1]{\text{ #1 }}

(Literal spaces inside are the same as \ outside, I believe.) Another option might be

\newcommand*{\textop}[1]{\mathbin{\text{#1}}}
\newcommand*{\textrel}[1]{\mathrel{\text{#1}}}

Then \textop{foo} would set foo as a binary operator, and \textrel{bar} would set bar as a binary relation. I'm not sure how this spacing would look, though, but it might work for what you want.

Best Answer

Related Solutions

[Tex/LaTex] Ugly spacing around f in math mode

[Tex/LaTex] Spacing around \text{} in mathmode

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