http://detexify.kirelabs.org/classify.html

I decided it would be beneficial to post some articles that I had written and posted elsewhere quite long ago.  This idea came from someone asking me today “How to change the font of an article from computer modern to sans serif?” My brain went short for a while, until I realized that I indeed had written something about tex fonts previously and maybe the answer was there. It’s the first time I had recognized how useful these shits were to me.. (Honestly I have to admit that after finishing those posts I regretted wasting time on writing nothing useful at all.) So, anyways, I put some of these posts back in this blog.

PS: The answer to the above question of changing to sans serif fonts is a simply line of code:

\renewcommand{\rmdefault}{cmss}

In TeX, a font requires two definition/description files: a metric definition file (.tfm) as introduced in the previous post, and a glyph shape description file (.gf from METAFONT, .pfa/.pfb for printer fonts, etc). The TeX font metric file *.tfm only specifies the dimensions of each character in the font, as well as a list of kerning and ligature pairs. It does not tell how actually a character looks like. The shapes of the characters are only described in the glyph file. The output of a TeX file, *.dvi, merely contains information about a large number of bounding boxes and their relative positions. Hence, in order to print the document to paper or to screen, a dvi file has to be interpreted using a dvi driver with glyph definition in mind. dvips is one such driver. It converts a dvi file to a PostScript file. Yap, or xdvi, or other dvi previewers, are essentially dvi drivers. They assume glyph information, otherwise they have no way of rendering the fonts stored in *.dvi.

Indeed, a large part of fonts talked about in this post are no longer TeX fonts. TeX only recognizes fonts from .tfm files—bounding boxes and kerning informations. METAFONT can produce glyph files (.gf), but fonts we commonly used today are Adobe fonts (.afm), TrueType fonts (.ttf), etc. Corresponding tools are designed to convert these fonts into TeX font metrics, such as afm2tfm, ttf2tfm, recognized by the latex program, as well as into glyph files (ttf2pk, etc) used by the dvi drivers (dvips, Yap, xdvi, etc). The relationships are illustrated in the following figure. (I slightly cheat in the figure in that the Adobe font metric .afm will only be converted to TeX font metric .tfm, but no information is deduced for glyph file.)

[To be finished..]

When we compile a TeX source, such as using “latex helloworld.tex”, the latex program searches for the font definition file ‹enc›‹family›.fd according to the font encoding and family specification inside the LaTeX source, loads the encoding definition ‹enc›enc.def, and typesets each individual character by consulting the TeX font metric file ‹family›[‹size›].tfm. These three files are key to generating the output dvi file.

The font definition file ‹enc›‹family›.fd simply declares the existence of some font, and provides a pointer to the metric file that the latex program should consult when typesetting the document. For example, in the txfont package, which provides characters in the Adobe Times font for both texts and formulas, there is one file t1txr.fd defining the txr font family using T1 encoding. The second and third commands read:

\DeclareFontFamily{T1}{txr}{}
\DeclareFontShape{T1}{txr}{m}{n}{t1xr}{}

It essentially says that a txr font with T1 encoding is defined. Whenever a T1 txr medium normal font is requested, LaTeX should use the t1xr.tfm metric file for all font sizes ( means “for all sizes”).

The corresponding encoding definition file ‹enc›enc.def defines the encoding. Let us see an example first to have an idea about what “encoding” means. In t1enc.def, there are four lines saying:

\DeclareFontEncoding{T1}{}{}
\DeclareTextAccent{\'}{T1}{1}
\DeclareTextSymbol{\ae}{T1}{230}
\DeclareTextComposite{\"}{T1}{a}{228}

The first line declares the existence of T1 encoding. The following lines mean that when this encoding is in effect the \'{x} command should superimpose character 1 (accent acute) over the character x, that \ae should produce character 230 (the æ ligature), and that \"a should produce character 228 (the umlaut ä). It would be much clearer to compare the above three commands with the corresponding ones in OT1 encoding (ot1enc.def):

\DeclareTextAccent{\'}{OT1}{19}
\DeclareTextSymbol{\ae}{OT1}{26}
(no composite command \"a defined)

One can see that, under different encodings, the same character has different indices in the character table. The same command can be issued to reference the same character, while it’s also possible that some characters exist in one encoding but not in the other. The encoding defined in LY1enc.def used by Y&Y TeX systems allows access to all the characters in a standard Adobe roman font.

Finally, the TeX font metric file ‹family›[‹size›].tfm is a binary file that defines width, depth, and height of each character, as well as the kerning pairs and ligature substitutions to be used with the font. LaTeX consults the tfm file to decide where to put characters when typesetting. The tfm file name has an optional [‹size›] field. For example, the cmr family has metric files cmr5.tfm, cmr6.tfm, cmr7.tfm, cmr8.tfm, cmr8.tfm, cmr10.tfm, cmr12.tfm, and cmr17.tfm. Each file fine tunes the size of each character and is used when different font sizes are correspondingly declared.

To summarize, when typesetting the document, latex requires three important files to get the correct encoding and character size information. Latex computes the locations of each character and outputs the dvi file.

Maybe You never worry about fonts. Right, since for most people Computer Modern or Times are perfect enough to make a pdf document look good. And what’s more, seldom would there have been LaTeX tutorials covering topics on fonts. Fonts are considered for TeXhackers, not for TeX users.

On the other hand, people who are interested in typography care too much about font looks. Even a person who has just installed a brand new Windows system will proceed to his first configuration task: use ClearType to antialiase screen fonts rendering (Well, this post was written at the time of Windows XP. Things have changed dramatically since then). Let alone Unix/Linux fans and TeX/LaTeX zealots.

This series of articles does not instruct one how to install fonts, neither does it teach specifically how to use different fonts in a LaTeX document. Instead, it gives a big picture about how fonts are dealt with behind the scene. Understanding the principals helps one on knowing, such as, “what affects the document’s texts”, rather than “what steps to take to improve the layout”. It is even conjectured that this article will soon be obsolete due to the new font schemes in LaTeX3.

Under the New Font Selection Scheme (NFSS) for LaTeX2e, a font has five attributes: encoding, family, series, shape, and size. For example, OT1/cmr/m/n/10 means that the document is using a font in OT1 encoding scheme, computer modern roman (cmr) family, medium weight (m) series, normal upright (n) shape, and 10pt size. These five parameters will be displayed whenever LaTeX gives an overfull box warning.

To change the current font layout, one can use a series of \font... commands, followed by a \selectfont activation. Example:

\fontencoding{T1}
\fontfamily{ptm}
\fontseries{b}
\fontshape{it}
\fontsize{12}{15}
\selectfont


It instructs LaTeX to use bold italic 12pt ptm font with 15pt baselineskip in the T1 encoding scheme for the texts. ptm is the widely used Adobe Times font, as oppose to cm.. (computer modern) families which might be hardly popular outside the TeX world.

Just to give a sense of what values are possible for each attribute in a font:

Encoding: OT1, T1…
Family: cmr, cmss, cmtt (computer modern); ptm, phv, pcr (Adobe)…
Series: m (medium), b (bold), bx (bold extended), sb (semi-bold), c (condensed)
Shape: n (normal/upright), it (italic), sl (slanted), sc (small caps)
Size: 5pt, 9pt, 10pt, 12pt, 14.4pt, 24.88pt…

Note that not all combinations of the attributes are valid.

Besides the above lower-level commands, LaTeX provides default settings for each document class. One can use different fonts by renewcommand‘ing the defaults. For example, \familydefault is originally set as \rmdefault, which in turn is set as cmr. One can issue a command like:

\renewcommand{\rmdefault}{phv}

to use Adobe Helvetica (phv) as the default font face. Changing \seriesdefault and \shapedefault are similar. However, font size has to be changed in a different way, e.g.:

\renewcommand{\normalsize}{\fontsize{12}{14.4}\selectfont}

This sets a 12pt font size. Font encoding is usually changed by using a different package, such as:

\usepackage[T1]{fontenc}

This forces a T1 encoding.

To summarize, a font in LaTeX is specified by five attributes. Except for the encoding, the other four should be intuitive to gentle users. There are specific commands to select a different font. The encoding scheme shall be discussed in the next article. A last note is that all the above values mentioned in this article are for text fonts. Math uses different fonts and values, and needs to be dealt with additionally. But the principals are the same. There are also some tailored packages designed to set a specific font for everything (including text and math), such as mathptmx, courier, avant. Readers are encouraged to explore these packages.

The following rules apply when using LaTeX2e…

• In display math mode, use \[ ... \] instead of $$ ... $$.

$$... $$ is simply obsolete.

• Use \textbf, \textit instead of \bf, \it.

\bf, \it are obsolete font selection commands. Under New Font Selection Scheme (NFSS), they should be replaced with \textbf, \textit. One immediate difference is that {\it\bf blabla} will not generate the composite effect of italic shape and bold series, while \textit{\textbf{blabla}} indeed produces bold italic fonts.

• Put a tilde before references or citations, e.g., Jie~\cite{habit06}.

This prevents LaTeX from putting a line break between the word and the citation. Similar cases are: length~$l$, function~$f(x)$, etc.

• Be cautious when changing the page margin and page layout.

Studies show that articles with approximately 66 characters per line are the most readable. Reading would become difficult if putting more and more texts into each line. That’s why you see articles are typeset in multiple columns in a newspaper.

• Differentiate between text comma and math comma, e.g., type “for $x=a$, $b$, or~$c$” instead of “for $x=a,b$, or $c$”.

A line will not break at math comma. That is why sometimes you see an ugly math expression exceeding the right margin of your texts. Also there will not be a white space after the math comma. Hence, in $x=a,b$, the “b” character is so close to the comma, which is unpleasant.

• Use \emph more often than \textit when you mean to emphasize a term or a phase.

You can easily change the layout of the emphasized content (such as to bold fonts instead of italic fonts) by redefining the \emph command. However, if you use \textit, you will meet a lot of hassles when you want to change the layout.

• Put a backslash after a dot if the dot does not mean full stop.

Example: “Please see p.\ 381 for an illustration.” The backslash after “p.” reminds LaTeX that the dot does not mean the end of a sentence, so LaTeX will put a correct white space between the dot and the number 381. Usually the width of the white space is shorter than that between a full stop and the beginning character of the next sentence. More examples are “Mr.\ Xing”, “e.g.\”, and “i.e.\”.

(Corrected: Well, none of the above examples are correct… They should be: “p.~381”, “Mr.~Xing”, “e.g.,”, “i.e.,”. But I am sure that the principle itself is ok. Anyone has a good example?)

• Note the difference between hyphen, en dash, em dash, and a minus sign.

Hyphen (-) connects the two parts of a compound word, such as in “anti-virus”. En dash (--) connects two numbers that define a range, such as in “pages 1--10”. Em dash (---) is a punctuation dash. And remember that when you write a negative number, embrace it by the dollar signs, e.g., $-40$.

• Write ellipsis using \ldots instead of three dots.

The \ldots commands correctly typeset the spaces between two consecutive dots.

The other day I ran into a person who’s asking people to draw the five Olympics rings by writing latex source codes only. I said, well, I could do that, using pstricks, which was my favorite drawing tool in latex.

After inspecting the Olympics logo for a while, I had a rough idea how to draw it. The key was to draw the five rings in the order: blue, yellow, black, green, and red. For each ring, draw a circle at that color with a certain line width, and then surround the circle with two white slim circles. This gave the salient pattern of the five rings and at the intersection of two rings some whites. The rest of the job was to make the interleaving effect of the five rings instead of seeing the yellow ring placed above the blue ring and so on. The trick was, after drawing the blue and the yellow rings, draw a blue arc at the place where the blue should be on top of the yellow at one of the intersection of the two rings. For the rest of the rings, do the same trick. Drawing the arcs was almost the same as drawing the rings (a colored circle squeezed by two slim white circles), except that an arc was part of a circle from some degree to some degree.

Okay, enough explanation. Here are the pstricks codes.

% This file draws the Olympic rings using PSTricks.
% File name: rings.tex
% Compile:
%  $ latex rings
%  $ dvips rings -E -o rings.eps
%  $ eps2png -width 600 rings.eps

\documentclass{article}
\usepackage[dvipsnames]{pstricks}
\pagestyle{empty}

\definecolor{myblue}{rgb}{0,.52,.78}
\definecolor{myyellow}{rgb}{.96,.76,0}
\definecolor{mygreen}{rgb}{0,.62,.24}
\definecolor{myred}{rgb}{.87,0,.14}

\newcommand{\drawring}[1]{%
\pscircle[linewidth=.25,linecolor=#1](0,0){1.375}%
\pscircle[linewidth=.05,linecolor=white](0,0){1.425}%
\pscircle[linewidth=.05,linecolor=white](0,0){1.125}%
}

\newcommand{\drawarc}[3]{%
\psarc[linewidth=.25,linecolor=#1](0,0){1.25}{#2}{#3}%
\psarc[linewidth=.05,linecolor=white](0,0){1.4}{#2}{#3}%
\psarc[linewidth=.05,linecolor=white](0,0){1.1}{#2}{#3}%
}

\begin{document}

\color{white}
\fboxsep=0pt
\fbox{

\begin{pspicture}(-4.5,-3)(4.5,1.5)
%\psgrid
\rput(-3,0){\drawring{myblue}}
\rput(-1.5,-1.375){\drawring{myyellow}}
\rput(-3,0){\drawarc{myblue}{330}{30}}
\rput(0,0){\drawring{black}}
\rput(-1.5,-1.375){\drawarc{myyellow}{30}{90}}
\rput(1.5,-1.375){\drawring{mygreen}}
\rput(0,0){\drawarc{black}{330}{30}}
\rput(3,0){\drawring{myred}}
\rput(1.5,-1.375){\drawarc{mygreen}{30}{90}}

\end{pspicture}

}
\end{document}


And this is the result:

Oh, by the way, remember the day this post was initialized, Aug 8, 2008. It’s the day for which we Chinese have been dreaming for years.

A = [0.0031 1 0 0 0 0 0 0
0 0.0031 1 0 0 0 0 0
0 0 0.0031 1 0 0 0 0
0 0 0 0.0031 1 0 0 0
0 0 0 0 0.0031 1 0 0
0 0 0 0 0 0.0031 1 0
0 0 0 0 0 0 0.0031 1
0 0 0 0 0 0 0 0.0031];

Matlab says that its numeric rank is 7.

The interesting thing is that A is a Jordan block!

Suppose I have a cell array which looks like this:


C =
[] [] []
[] [] [3x3 double]
[] [] []

How can I get all the empty cells using as few commands as possible? Well, the answer is …

cellfun(@isempty, C)

So, cellfun is a function that applies a function (isempty here) to each cell of a cell array (C here). If you enjoy general Matlab functions that implicitly apply to each element of an array (say, sqrt(M) does the square roots to all the elements of M), then you must also enjoy this cellfun function that applies an arbitrary function to each element of a cell array. Check it out!

整理了一下。忘记了也有地方可以查

Math spacing:

Lengths defined relative to characters:

Physical lengths (commonly used):

Physical lengths (not so commonly used):