How can I label the columns and rows of a matrix?

Questions
1

I would like to label the columns and rows of a matrix (e.g. I, J, K, L and M) and ideally also provide an overall label for the rows (winner) and the columns (loser).

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The corresponding functionality (at least for the column and row labels) seems to be in LaTeX through a variety of packages, e.g. matrices - Matrix with rows and columns labeled - TeX - LaTeX Stack Exchange

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2

You may use table to recreate the matrix structure.

$ 
#table(
    columns: (auto,)+(3pt,)+(auto,)*5+(3pt,),
    stroke: none,
    align: (right + horizon,) + (center + horizon,)*7,
    [],[], $I$, $J$, $K$, $L$, $M$, [],
    $I$, table.cell(rowspan: 5, box(stroke: none, inset: (top: -0.5em), $lr("[", size: #875%)$)), $0$, $1$, $0$, $1$, $0$, table.cell(rowspan: 5, box(stroke: none, inset: (top: -0.5em), $lr("]", size: #875%)$)),
    $J$, $0$, $0$, $1$, $0$, $1$,
    [winner  $K$], $1$, $0$, $0$, $1$, $1$,
    $L$, $0$, $1$, $0$, $0$, $0$,
    $M$, $0$, $0$, $0$, $1$, $0$,
  )
 $

I don’t know a method that can automatically adjust the size of delimiters.

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3

Thanks for this solution; it does add the ‘winner’ but not the ‘loser’ (but presumably I could do that above the ‘K’ somehow).

It hadn’t occurred to me that I would be able to get the delimiters using a table but your solution is interesting and I could possibly adapt it so the size is calculated programmatically.

4

There is another solution using the pin-it package. Please check out my reply How to input an excess matrix, where elements "overflow" the parentheses? - #7 by Fe_Y.

5

Going off of @Fe_Y’s code, you might dynamically set the delimiter height with an approach like this:

#let labelmat(
  collabels,
  rowlabels,
  ..args
) = context {
  let numcols = collabels.len()
  let numrows = rowlabels.len()
  let matentries = args.pos().chunks(numcols)
  let matheight = matentries.map(
    row => calc.max(..row.map(i => measure(i).height))
  ).sum() + 10pt * numrows
  let delimcell(delim) = table.cell(
    rowspan: numrows, 
    box(inset: (top: -5pt, left: -5pt), $lr(delim, size: #matheight)$)
  )
  table(
    columns: (auto, 7pt, ..(auto,) * numcols, 7pt),
    stroke: none,
    ..args.named(),
    [], [], ..collabels, [],
    ..for (rowindx, (rowlab, rowentries)) in rowlabels.zip(matentries).enumerate() {(
      rowlab,
      ..if rowindx == 0 {(delimcell($\[$),)},
      ..rowentries,
      ..if rowindx == 0 {(delimcell($\]$),)},
    )},
  )
}

#labelmat(
  ("a", "b", "c"),
  ("d", "e", "f"),
  $alpha_r display(beta_s / delta)$, $0$, $1$,
  $1$, $2$, $display(sum_2^n i^2)$,
  $1$, $2$, $3$,
  align: center + horizon
)

Screenshot 2025-05-06 at 3.36.12 PM

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