Previous: Function Headers, Up: Tips and Standards
As noted above, documentation is typically in a commented header block on an Octave function following the copyright statement. The help string shown above is an unformatted string and will be displayed as is by Octave. Here are some tips for the writing of documentation strings.
The documentation string can have additional lines that expand on the details of how to use the function or variable. The additional lines should also be made up of complete sentences.
However, rather than simply filling the entire documentation string, you can make it much more readable by choosing line breaks with care. Use blank lines between topics if the documentation string is long.
/ refers to its second argument as `DIVISOR', because the
actual argument name is divisor.
Also use all caps for meta-syntactic variables, such as when you show the decomposition of a list or vector into subunits, some of which may vary.
Octave also allows extensive formatting of the help string of functions using Texinfo. The effect on the online documentation is relatively small, but makes the help string of functions conform to the help of Octave's own functions. However, the effect on the appearance of printed or online documentation will be greatly improved.
The fundamental building block of Texinfo documentation strings is the
Texinfo-macro @deftypefn, which takes three arguments: The class
the function is in, its output arguments, and the function's
signature. Typical classes for functions include Function File
for standard Octave functions, and Loadable Function for
dynamically linked functions. A skeletal Texinfo documentation string
therefore looks like this
-*- texinfo -*-
@deftypefn{Function File} {@var{ret} =} fn (...)
@cindex index term
Help text in Texinfo format. Code samples should be marked
like @code{sample of code} and variables should be marked
as @var{variable}.
@seealso{fn2}
@end deftypefn
This help string must be commented in user functions, or in the help
string of the DEFUN_DLD macro for dynamically loadable
functions. The important aspects of the documentation string are
Texinfo format has been designed to generate output for online viewing with text terminals as well as generating high-quality printed output. To these ends, Texinfo has commands which control the diversion of parts of the document into a particular output processor. Three formats are of importance: info, html and TeX. These are selected with
@ifinfo
Text area for info only
@end ifinfo
@ifhtml
Text area for HTML only
@end ifhtml
@tex
Text area for TeX only
@end tex
Note that often TeX output can be used in html documents and so often
the @ifhtml blocks are unnecessary. If no specific output
processor is chosen, by default, the text goes into all output
processors. It is usual to have the above blocks in pairs to allow the
same information to be conveyed in all output formats, but with a
different markup. Currently, most Octave documentation only makes a
distinction between TeX and all other formats. Therefore, the
following construct is seen repeatedly.
@tex
text for TeX only
@end tex
@ifnottex
text for info, HTML, plaintext
@end ifnottex
Another important feature of Texinfo that is often used in Octave help
strings is the @example environment. An example of its use is
@example
@group
@code{2 * 2}
@result{} 4
@end group
@end example
which produces
2 * 2
=> 4
The @group block prevents the example from being split across a
page boundary, while the @result{} macro produces a right
arrow signifying the result of a command. If your example is larger than
20 lines it is better NOT to use grouping so that a reasonable page boundary
can be calculated.
In many cases a function has multiple ways in which it can be called,
and the @deftypefnx macro can be used to give alternatives. For
example
-*- texinfo -*-
@deftypefn{Function File} {@var{a} =} fn (@var{x}, ...)
@deftypefnx{Function File} {@var{a} =} fn (@var{y}, ...)
Help text in Texinfo format.
@end deftypefn
Many complete examples of Texinfo documentation can be taken from the
help strings for the Octave functions themselves. A relatively complete
example of which is the nchoosek function. The Texinfo
documentation string for nchoosek is
-*- texinfo -*-
@deftypefn {Function File} {} nchoosek (@var{n}, @var{k})
Compute the binomial coefficient or all combinations of
@var{n}. If @var{n} is a scalar then, calculate the
binomial coefficient of @var{n} and @var{k}, defined as
@tex
$$
{n \choose k} = {n (n-1) (n-2) \cdots (n-k+1) \over k!}
$$
@end tex
@ifnottex
@example
@group
/ \
| n | n (n-1) (n-2) ... (n-k+1)
| | = -------------------------
| k | k!
\ /
@end group
@end example
@end ifnottex
If @var{n} is a vector, this generates all combinations
of the elements of @var{n}, taken @var{k} at a time,
one row per combination. The resulting @var{c} has size
@code{[nchoosek (length (@var{n}),@var{k}), @var{k}]}.
@code{nchoosek} works only for non-negative integer arguments; use
@code{bincoeff} for non-integer scalar arguments and for using vector
arguments to compute many coefficients at once.
@seealso{bincoeff}
@end deftypefn
which demonstrates most of the concepts discussed above.