B.7 |
Mathematical Formulas |
|
B.7.1 |
Math Mode Environment |
|
The three ways to use math mode ($
...$
,
\(
...\)
and
\begin{math}
...\end{math}
) are supported.
The three ways to use display math mode ($$
...$$
,
\[
...\]
and
\begin{displaymath}
... \end{displaymath}
) are also
supported.
Furthermore, \ensuremath
behaves as expected.
The equation
, eqnarray
, eqnarray*
environments
are supported.
Equation labeling and numbering is performed in the first two
environments, using the equation
counter.
Additionally, numbering can be suppressed in one row of an
eqnarray
, using the \nonumber
command.
Math mode is not as powerful in HEVEA as in LATEX. The
limitations of math mode can often be surpassed by using math display
mode. As a matter of fact, math mode is for in-text formulas. From
the HTML point of view, this means that math mode does not close
the current flow of text and that formulas in math mode must be
rendered using text-level elements only. By contrast, displayed
formulas can be rendered using block-level elements. This means that
HEVEA have much more possibilities in display context than inside
normal flow of text. In particular, stacking text elements one above
the over is possible only in display context.
For instance compare how HEVEA renders
$\frac{1}{\sum_{i=1}^{\infty}$
as: 1/åi=1¥ ii, and
$$\frac{1}{\sum_{i=1}^{\infty}$$
as:
HEVEA admits, subscript (_
), superscripts (^
) and
fractions (\frac{
numer}{
denom}
).
The best effect is obtained in display mode, where HTML
TABLE
element is extensively used.
By contrast, when not in display mode, HEVEA uses only
SUB
and SUP
text-level elements to render superscrits
and subscript, and the result may not be very satisfying.
However,
simple subscripts and superscripts, such as x_i
or x^2
,
are always rendered using the SUB
and SUP
text-level elements and their appearance should be correct
even in in-text formulas.
When occurring outside math mode, characters _
and ^
act as
ordinary characters and get echoed to the output. However, a warning
is issued.
The nth root command \sqrt
is not supported.
The ``root'' symbol is not necessary, thanks
to fractional exponents. For instance, the \sqrt
command can be
defined as follows:
\newcommand{\sqrt}[2][2]{\left(#2\right)^{1/#1}}
Then, the source
fragment: $$\sqrt[3]{\frac{1}{n!}} + \sqrt{\pi}$$
gets rendered
as follows:
An attempt is made to render all ellipsis constructs (\ldots
,
\cdots
, \vdots
and \ddots
). The effect may be
strange for the latter two.
B.7.3 |
Mathematical symbols |
|
Symbols that can be printed using browser iso-latin1 or symbol fonts
are translated.
Other symbols are undefined most of the time.
Attempting to translate them will thus generate ``Unknown macro''
warnings.
Then, users can choose their own replacement for these symbols.
These personal definitions are best placed in an ad-hoc style file,
given as a command line argument to HEVEA.
A suggested replacement is a mix of colors and available
symbols.
For instance, HEVEA cannot render the \leadsto
symbol, but it
can be defined as a red arrow by:
\newcommand{\leadsto}{{\red\rightarrow}}
Then, $$A \leadsto B$$
is rendered as follows:
A ® B
When given the -nosymb
option, HEVEA silently replaces
symbols that cannot be rendered by iso-latin1 only by text equivalents.
These equivalents are English words by default, or French words when the
-francais
option is set.
Log-like functions and variable sized-symbols are recognized and their
subscripts and superscripts are put where they should in display mode.
Subscript and superscript placement can be changed using the
\limits
and \nolimits
commands.
Big delimiters are also handled.
B.7.4 |
Putting one thing above the other |
|
The commands \stackrel
, \underline
and \overline
are recognized.
They produce sensible output in display mode.
In text mode, these macros call the \textstackrel
,
\textunderline
and \textoverline
macros.
These macros perform the following default actions, which can be
changed by redefining them:
-
\textstackrel
- Performs ordinary superscripting.
- \textunderline
- Underlines its argument, using the
U
text-level element.
- \textoverline
- Sends a warning message to the
console and echoes its argument in the output.
Math accents (\hat
, \tilde
, etc.) are not
handled by default.
However, the distribution includes a mathaccents.hva file
that provides definitions for almost all math accents commands,
except \check
and \breve
.
Rendering is far from perfect and changes from display to text mode.
More precisely, the accent is put (too far) above the symbol in display mode,
and as an ordinary superscript in text mode.
For instance, given the formula
\tilde{v} \cdot \vec{U}
, we get
``v~ · U®'' in text mode and
in display mode.
If such a rendering is considered too ugly,
one should not load the mathaccents.hva file and write
alternative definitions.
For instance, the following custom definitions
issue color changes:
\newcommand{\tilde}[1]{{\blue#1}}
\newcommand{\vec}[1]{{\red#1}}
With such definitions the previous example now appears as:
we get
``v · U'' in text mode and
v · U
in display mode.
Of course, such a trick probably requires looking closely at HTML
output to check whether the document is still understandable or not.
It may be better to stay with a poorly formatted document that remains
closer to universally understood notations for mathematics.
By contrast with LATEX, space in the input matters in math mode.
One or more spaces are translated to one space.
Furthermore,
spaces after commands (such as \alpha
) are echoed
except for invisible commands (such as \tt
).
This allows users to control space in their formulas, output being
near to what can be expected.
Explicit spacing commands (\,
, \!
, \:
and
\;
) are recognized, the first two commands do nothing, while
the others two output one space.
Letters are italicized inside math mode and this cannot be
changed. The appearance of
other symbols can be changed using
LATEX 2e style changing commands (\mathbf
, etc.).
The commands \boldmath
and \unboldmath
are not
recognized. Whether symbols belonging to the symbol font are affected
by style changes or not is browser dependent.
The \cal
declaration and the \mathcal
commands (that
yield calligraphic letters in LATEX) exist. They yield red letters by
default.
Observe that this does not corresponds directly to how LATEX manage style
in math mode and that, in fact, style cannot really change in math mode.
Math style changing declarations \displaystyle
and
\textstyle
do nothing when HEVEA is already in the requested
mode,
otherwise they issue a warning.
This is so because HEVEA implements displayed maths as tables,
which require to be both opened and closed and introduce line breaks
in the output.
As a consequence, warning on \displaystyle
are to be taken seriously.
The commands \scriptstyle
and \scriptscriptstyle
perform type size changes.