Guide to LaTeX (4th Edition) (Tools and Techniques

144 Chapter 5. Mathematical Formulas
5.4.10 International typesetting standards
The International Standards Organization (ISO) has established the recognized
! conventions for typesetting mathematics, the essential elements of which are
presented in an article by Beccari (1997), along with a description of how they
may be realized with L AT E X. Some of these rules have already been mentioned and
demonstrated in the examples. Here are the major points.
1. Simple variables are represented by italic letters, as a b c x y z.
2. Vectors are written in bold face italic, as B v ω.
3. Tensors of 2nd order and matrices may appear in a sans serif font, as
M D I.
4. The special numbers e, i, π, as well as the differential operator d, are to be
written in an upright font to emphasize that they are not variables.
5. A measurement consisting of a number plus a dimension is an indivisible
unit, with a smaller than normal space between them, as 5.3 km and 62 kg.
The dimension is in an upright font.
Point 1 is fulfilled automatically by L AT E X. Point 5 is easily achieved by inserting
the small space \, command between the number and dimension, as 5.3\,km
and 62\,kg. Using the protected space ˜ instead is very common practice among
L AT E X users, which ensures that the two parts are not split, but with regular, not
small spacing: 5.3 km and 62 kg.
Point 2 is not satisfied with the \vec command, which produces B. Nor does
\mathbf help, for this yields B, in an upright font. The best solution is to use
the \boldsymbol command from the A M S package amsbsy (Section 12.2.1) or
the \bm command from the tools package bm (Section B.5.4). Otherwise one must
resort to defining
\renewcommand{\vec}[1]{\mbox{\boldmath$#1$}}
for a revised \vec command.
Similarly point 3 can be met with the math alphabet command \mathsf.
However, Beccari does point out that even tensor variables should probably be
italic. This is more difficult, but it can be accomplished. See example 5 on
page 191.
Point 4 is the one that is most often violated, especially for the differential d.
We have demonstrated it in the examples in this book and have shown how it may
be achieved with the \mathrm math alphabet command. However, to simplify the
application, it is recommended to create some user-defined commands, such as
\newcommand{\me}{\mathrm{e}} for math e
\newcommand{\mi}{\mathrm{i}} for math i
\newcommand{\dif}{\mathrm{d}} for differential operator d
An upright π is not so easy since this is not provided in the usual math fonts.
With these new commands, the equation on page 119 is more conveniently
set with
\[ \intˆ{\infty}_0 f(x)\,\dif x \approx
\sumˆn_{i=1}w_i \meˆ{x_i} f(x_i) \]