A matrix representation of certain matrix in LaTeX

Question

How  can  we  write the following  statement with  the  matrix  form  in the  LaTeX  ? (We  wish  to  represent  it  in the  matrix  form)

By $delta_{ij}(a)$  we mean a n by n matrices 
in $M_n(mathbb{R})$ which has only one nonzero 
entry $a$ at $i$, th row and j th column.

Bernard · Accepted Answer

If I understand well, is it something like this you want?

documentclass{article}
usepackage{fourier}
usepackage{amsmath}
usepackage{blkarray, bigstrut}

begin{document}

begin{equation*}
  begin{blockarray}{rl@{}c@{}r}
    & & makebox[0pt]{column $j$} [-0.5ex]
    & & ,downarrow [-0.5ex]
    begin{block}{r(l@{}c@{}r)}
    & makebox[3.1em]{Large $0$bigstrut[t]} & vdots &makebox[4.2em]{Large $0$} [-0.2ex]
    text{row }i to mkern-9mu & raisebox{0.5ex}{makebox[3.2em][l]{dotfill}} & 1 & raisebox{0.5ex}{makebox[4.2em][r]{dotfill}} [-1ex]
    & makebox[3.1em]{Large $0$} & vdots &makebox[4.2em]{bigstrutLarge $0$} 
    end{block}
  end{blockarray}
end{equation*}

end{document}

F. Pantigny · Answer

With {NiceMatrix} of the package nicematrix.
documentclass{article}
usepackage{nicematrix}
usepackage{tikz}

begin{document}

NewDocumentCommand{zero}{}{Block{}<Large>{0}}

$begin{NiceMatrix}[nullify-dots,columns-width=4mm,xdots/shorten=5pt]
CodeBefore
  SubMatrix({3-2}{5-4})
Body
                  &        & clap{column $j$}   
                  &        & downarrow          [1mm]
                  & zero  & Vdots     & zero  
text{row } i to & Cdots & 1          & Cdots 
                  & zero  & Vdots     & zero 
end{NiceMatrix}$

end{document}

You need several compilations (because nicematrix uses PGF/Tikz nodes under the hood).

A matrix representation of certain matrix in LaTeX

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