Horizontal Line in Array

Question

Good evening,
I'm trying to achieve following picture in latex, but i can't do it. Can someone help me?

This is what I have so far:
documentclass[a4paper,12pt]{scrartcl}

usepackage{booktabs}
usepackage[utf8] {inputenc}
usepackage[ngerman]{babel}
usepackage{amsmath}
usepackage{amssymb}
usepackage{amsfonts}
usepackage[T1]{fontenc}

begin{document}

begin{center}
      $left(begin{array}{rrrr}
             2&2&-1&3  
            cmidrule{2-4}
             0&1&3&4  
             0&1&3&4  
             0&3&9&6  
             0&1&3&-2  
    end{array}right)$
end{center}

end{document}

Werner · Accepted Answer

You're missing the vertical line | in the column specification and a multicolumn{1}{r} for the element in the top left corner:

documentclass{article}

begin{document}

[
  left(
    begin{array}{ r | *{3}{r} }
      multicolumn{1}{r}{2} & 2 & -1 &  3 
      cline{2-4}
      0 & 1 &  3 &  4 
      0 & 1 &  3 &  4 
      0 & 3 &  9 &  6 
      0 & 1 &  3 & -2  
    end{array}
  right)
]

end{document}

For a more evenly distributed spacing around the last three columns, consider using phantom{-}2 in the first row:

documentclass{article}

begin{document}

[
  left(
    begin{array}{ r | *{3}{r} }
      multicolumn{1}{r}{2} & phantom{-}2 & -1 &  3 
      cline{2-4}
      0 & 1 &  3 &  4 
      0 & 1 &  3 &  4 
      0 & 3 &  9 &  6 
      0 & 1 &  3 & -2  
    end{array}
  right)
]

end{document}

F. Pantigny · Answer

With nicematrix. The environments of nicematrix create PGF/Tikz nodes under the rows, columns and cells and the array and it's possible to use them to draw whatever you want with Tikz.
documentclass{article}
usepackage{nicematrix}
usepackage{tikz}

begin{document}

[
begin{pNiceMatrix}[r,right-margin,columns-width=auto]
  2 & 2 & -1 &  3 
  0 & 1 &  3 &  4 
  0 & 1 &  3 &  4 
  0 & 3 &  9 &  6 
  0 & 1 &  3 & -2  
CodeAfter
tikz draw ([xshift=4pt]row-6-|col-2) |- (row-2-|col-5) ;
end{pNiceMatrix}
]

end{document}

Horizontal Line in Array

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