# Matrix column spacing

I am using a matrix in Plain TeX, and the spacing between columns is too large. Since I'm also changing the paper size, the matrix runs off the side of the page. A minimal example is

\input eplain

$$A = \left\{ \matrix{ (1&1&(1&0&0)^6&||&1&1&1&1&1&1&1&1&1&1&1&1&1&1&1^{30})\cr (1&1&(1&0&0)^6&||&1&1&1&1&1&1&1&1&1&1&1&1&1&1&1^{30})\cr (1&1&(1&0&0)^6&||&1&1&1&1&1&1&1&1&1&1&1&1&1&1&1^{30})\cr (1&1&(1&0&0)^6&||&1&1&1&1&1&1&1&1&1&1&1&1&1&1&1^{30})\cr } \right\}$$

\bye


I can shrink the columns by inserting an \hskip before each &, but that makes the source difficult to read. Is there a nicer way to control this spacing?

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This is Plain, not eplain. The definition of \matrix uses \quad between columns. You can define a new macro that takes another argument for the spacing:

\input eplain
\catcode@=11
\def\xmatrix#1#2{\null\,\vcenter{\normalbaselines\m@th
\ialign{\hfil$##$\hfil&&\hskip#1\hfil$##$\hfil\crcr
\mathstrut\crcr\noalign{\kern-\baselineskip}
#2\crcr\mathstrut\crcr\noalign{\kern-\baselineskip}}}\,}
\catcode@=12

$$A = \left\{ \xmatrix{3pt}{ (1&1&(1&0&0)^6&||&1&1&1&1&1&1&1&1&1&1&1&1&1&1&1^{30})\cr (1&1&(1&0&0)^6&||&1&1&1&1&1&1&1&1&1&1&1&1&1&1&1^{30})\cr (1&1&(1&0&0)^6&||&1&1&1&1&1&1&1&1&1&1&1&1&1&1&1^{30})\cr (1&1&(1&0&0)^6&||&1&1&1&1&1&1&1&1&1&1&1&1&1&1&1^{30})\cr } \right\}$$

\bye


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You can redefine \quad inside the group; this way, it is restored when the group is complete (originally, I had it redefined before the group and reset it manually after the group; thanks to morbusg for the reminder, saving me two lines of code).

\input eplain
$$\def\quad{\hskip1ex\relax} A = \left\{ \matrix{ (1&1&(1&0&0)^6&||&1&1&1&1&1&1&1&1&1&1&1&1&1&1&1^{30})\cr (1&1&(1&0&0)^6&||&1&1&1&1&1&1&1&1&1&1&1&1&1&1&1^{30})\cr (1&1&(1&0&0)^6&||&1&1&1&1&1&1&1&1&1&1&1&1&1&1&1^{30})\cr (1&1&(1&0&0)^6&||&1&1&1&1&1&1&1&1&1&1&1&1&1&1&1^{30})\cr } \right\}$$
\bye


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You could redefine the \quad inside the display, because it forms a group, the redefinition goes away automatically after the group (ie. $$\let\quad\enspace ...$$) – morbusg Feb 12 '14 at 9:54