Math & Science ⇒ Arrays in plain TeX

[tex_eugene]

I don't think the environment {array} is being defined in TeX, can someone help me to translate the following LaTeX to TeX please?

Code: Select all

\[
  f(n) = \left\{ 
  \begin{array}{l l}
    n/2 & \quad \text{if $n$ is even}\\
    -(n+1)/2 & \quad \text{if $n$ is odd}\\
  \end{array} \right.
\]

Thank you!

[Stefan Kottwitz]

You could use \halign for producing tables, such as

Code: Select all

\halign{#&#\cr
  one   & two \cr
  three & four \cr}
\end

Stefan

[cgnieder]

You might want to take a look in the texbook, especially chapters 17--20.

The following MWE

Code: Select all

$$
 f(n) = \cases{
   n/2      &\quad if $n$ is even \cr
   -(n+1)/2 &\quad if $n$ is odd \cr
 }
$$
\bye

gives

tex_cases.png (5.13 KiB) Viewed 4811 times

Regards

[Stefan Kottwitz]

Very good point! In the specific case it's the shortest way. I just wonder why plain TeX is required, which can be difficult if LaTeX's and amsmath's capabilties were desired.

Stefan

[cgnieder]

I wonder that, too. The only time I use plain TeX is when I'm intrigued to learn basic concepts of TeX or when I'm trying to understand underlying concepts of some LaTeX (kernel) code. This means: very seldomly...