This question has been bugging me for a long time: How do I properly typeset volume integrals? I would like to use the convention often used in Physics: d^3x=dV and \int dx f(x) instead of \int f(x) dx
Example:
The kinetic energy is simply given by \begin{equation} T = \int\,\mathrm{d}^3\mathbf{x}\frac{\rho}{2} \mathbf{\dot x}^2 = \frac{3}{10}M\dot R^2\;. \end{equation} But the integral looks somehow bad as the spacing between the x and the d is too big. How can I change this?
Maybe the following is what you're after:
I raised the 3 quite a bit and slightly moved it to the left; this way I could move the x much closer to the d. Here's the code for a command \d that takes one optional and one mandatory argument:
\documentclass{article} \usepackage{calc} \renewcommand*\d[2][]{% \mathrm{d}% \ifx\relax#1\relax\else \rule{-0.05em}{1.9ex}^{#1}\! \fi #2\, } \begin{document} \[ \int \d[3]{\mathbf{x}} \frac{\rho}{2} \mathbf{\dot x}^2 \qquad \int \d{\mathbf{y}} f(\mathbf{y}) \] \end{document} Note that this only works for "small" integration variables like x. Moreover, I removed the \, between \int and \mathrm{d} that you had and put it after the differential instead. You can of course adjust this to your needs.
x in \dot x is bold, than I'd also make it bold in the differential. (Personally, as a mathematician, I make neither of them bold.)
\!or\mkern. This may be useful or not: tex.stackexchange.com/questions/67912/large-negative-spaces