Note that it has to be square brackets. The big A can be normal size if necessary as long as it's still centered on the left. I could also live with it being below the outer matrix annotating the left hand side with curly braces.

  • 2
    Please help us help you and add a minimal working example (MWE) that illustrates your problem. Reproducing the problem and finding out what the issue is will be much easier when we see compilable code, starting with \documentclass{...} and ending with \end{document}. • Note this is a Q&A site, not a please do this for me service. What do you have so far. – albert Dec 11 '18 at 18:52

Something like this?



\begin{array}{ @{} c c : c c @{} }
  \begin{array}{ @{} ccc @{}}
  \phantom{1} \\ & \phantom{1} \\ && \phantom{1}
  \begin{array}{ @{} ccc @{}}
  1 \\ & 1 \\ && 1
\multicolumn{2}{c:}{\makebox[0pt]{\smash{\scalebox{5}{A}}}} && \ddots


enter image description here

After replacing \multicolumn{2}{c:}{...} by


the output will be

enter image description here

The amount of raising has been guessed. It may be computed, but I don't think you need such an object more than once.

|improve this answer|||||
  • This is really good. I didn't think of using \left[, \right[, and arrays at all. Though, can you also think of a way to center the A vertically? – Sebastian Oberhoff Dec 12 '18 at 1:16
  • 1
    @SebastianOberhoff Added. – egreg Dec 12 '18 at 8:33

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