4

I'd like to write integrals with the differential first, the way physicists tend to: $\int dx f(x)$. The problem is that this puts an unsightly (to my eye) gap between the integral sign and the differential, and then puts the integrand much too close to the differential. I can solve this by writing something like $\int \hskip -3pt dx\ f(x)$, but that is hardly satisfactory.

What is the accepted way to do this? Where should I be looking?

2
  • 5
    Tear down the walls of prejudice, be adventurous, follow your instincts, and simply don't write as they do.
    – percusse
    Apr 12, 2013 at 22:30
  • Welcome to TeX.SE. Apr 12, 2013 at 23:57

3 Answers 3

1

As a physicist, I'd like to give you this:

\newcommand*\diff{\mathop{}\!\!\mathrm{d}}
$\int \diff x f(x)$

\begin{equation}
    \int \diff x f(x)
\end{equation}

Although it doesn't look good in the $$-environment. Please note that it has to be d x and not dx.

1
  • But I think you don't get the space after the differential automatically. And you should care about how it looks in fractions and more.
    – Manuel
    Apr 13, 2013 at 9:58
1

Here's a possible definition, compared with the "default" output (\displaystyle is used only for showing the result without centering the formula). Note that you need different backspace in displays and in inline formulas.

\documentclass{article}

\newcommand\pred[1]{
  \mathchoice{\mkern-6mu}{\mkern-1mu}{}{}
  d#1\,
}

\begin{document}
$\displaystyle\int_a^b \pred{x} f(x)$ \quad
$\displaystyle\int_a^b dx\, f(x)$

\bigskip

$\int_a^b \pred{x} f(x)$ \quad
$\int_a^b dx\, f(x)$

\end{document}

enter image description here

4
  • As you wrote this command, shouldn't be better to enclose d#1 in a \mathit{d#1}? I'm not sure myself. The differential is written with two or more letters, but is one object.
    – Manuel
    Apr 13, 2013 at 10:01
  • @Manuel While "dx" is one object, it's still composed by two distinct symbols.
    – egreg
    Apr 13, 2013 at 10:03
  • If you had written it with \mathrm{d} then I should think about it as an operator and then I haven't said anything. But since you wrote it in italic I think that may be dx should be written similar to the identity function which I write as \mathit{id} instead of id.
    – Manuel
    Apr 13, 2013 at 10:09
  • @Manuel I don't agree with this: \mathit{id} is good because the two letters don't have a separate meaning. In this case x should be the same x as in f(x).
    – egreg
    Apr 13, 2013 at 10:22
0

What about the following?

\def\Int#1#2{\int \hskip -3pt d{#1}\ {#2}}

As far as I understand you want freezing the chosen skips.

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