Cioa vi riporto la risposta di Joseph Wright:
Hello Lorenzo,
I have to start by saying that this is not a bug, it’s a deliberate
design decision. I’ll explain the reasoning, but first I’ll point out
that for cases such as your own you can use the ‘table-parse-only’
option in siunitx version 2:
`\documentclass{article}
\usepackage{booktabs}
\usepackage{siunitx}
\sisetup{output-decimal-marker = {,},table-parse-only}
\begin{document}\begin{tabular}{cSSSS}
\toprule
$D$& {$P$}& {$u$}& {$\beta$}& {$G$} \\
(m)& {(kg)}& {(m)}& & {(Pa)} \\
\midrule
$5$& 269.8& 0.000674& 1.79& 0.04089 \\
$10$& 421.0& 0.001035& 3.59& 0.04089 \\
$20$& 640.2& 0.001565& 7.18& 0.04089 \\
\bottomrule
\end{tabular}\end{document}`
(Version 2 of siunitx was released about two months ago.)
The reason siunitx works in the way it does is because of the
information you need in order to lay out numbers aligning on decimal
markers. The default is to always put the marker at the middle of the
column, and to allow each side to expand flexibly. That is relatively
easy to do, as you only need a fill on both sides.However, life is much more complex when you want variable placement of
the marker. In your examples, you’ve got ‘nice’ columns where each entry
in a column has the same number of digits. For those, you can not worry
about controlling the alignment, which is why the ‘c’ column type works.
The ‘table-parse-only’ option does a very similar thing but with the
digit formatting of siunitx.siunitx can’t make the assumption that each column is ‘well behaved’.
There may be different numbers to print in each column, for example10.123
4.56
2.345So siunitx has to box things up to maintain alignment. That means that
it needs to know how many digits to allow for, hence the need for the
‘table-format’ option (known as ‘tabformat’ in version 1 of siunitx).
The way that tables are constructed by LaTeX means that this is not
available at the start of a column, hence needing it from the user as an
option. (I’ve thought about a two-pass automated system, but it’s a
complicated issue.)Regards,
Joseph
Aspetto la Tex Live 2010 per probare l’opzione table-parse-only di siunitx 2.0.
Ciao,
L.