Labeling and Double Labeling Matrices in LaTex (Overleaf) - useful for Markov chain transition matrices

In order to label a simple 3x3 matrix, you can either do it by columns/rows or give it a full title over the whole matrix.

This is the code for both the full titles and by each column/row:

begin{document}

begingroup
setlength{tabcolsep}{2pt} % sets spacing horizontally
renewcommand{arraystretch}{1} % sets spacing vertically
begin{tabular}{ c c c }

%===============================================================
%Row 1
%===============================================================
%Column 1
Top Title &

%Column 2
&

%Column 3



%===============================================================
%Row 2
%===============================================================
%Column 1
%this creates the horizontal array 
begingroup %make sure to use this to control spacing separately from the bigger array
setlength{tabcolsep}{6pt}
 begin{tabular}{cccc}
     1  & 2  & 3 
 end{tabular}
endgroup&

%Column 2
&

%Column 3


%===============================================================
%Row 3
%===============================================================

% Column 1
$begin{bmatrix}
    a & b & c 
    d & e & f 
    g & h & i 
end{bmatrix}$ &


%Column 2
% this creates the vertical array
begin{tabular}{ccc}
     x  y  z
 end{tabular} &
 
 

%Column 3
 Side Title 

end{tabular}
endgroup

end{document}

From this code you can adjust what titles you would like to keep/erase. Remember to adjust the matrix size accordingly. Matrices/tables/arrays have a syntax of:

Row1Column1 & Row1Column2     & ... & Row1Column(N) 

Row2Column1 & Row2Column2     & ... & Row2Column(N) 
.
.
.

Row(N)Column1 & Row(N)Column2 & ... & Row(N)Column(N)

So this is essentially a 3x3 matrix with the first column being:

• Big title (Top Title)
• column titles (1 2 3)
• matrix

Second Column:

• Empty space
• Empty space
• row titles (x y z)

Third Column:

• Empty space
• Empty space
• Big Title (Side title)

Welcome to TEX.SE! It's a nice approach. I use nicematrix package to do this.

documentclass{article}
usepackage{amsmath}
usepackage{nicematrix}
begin{document}
    begin{align*}
        begin{array}{cc}
            text{Top Title} & 
            begin{bNiceMatrix}[first-row,last-col]
                1 & 2 & 3 &     
                a & b & c & x   
                d & e & f & y   
                g & h & i & z   
            end{bNiceMatrix} &  text{Side Title}
        end{array}
    end{align*}
end{document}

Here I handled the matrix with exterior with bNiceMatrix environment.

Here is another way to do that with nicematrix. In the latest version (5.10 of 2021-02-05), there is a built-in command SubMatrix which I used to add the brackets in the array previously constructed.

documentclass{article}
usepackage{nicematrix}
begin{document}
$A = enskip 
begin{NiceMatrix}[baseline=4]
Block{1-3}{text{Top Title}} 
1 & 2 & 3 &  
a & b & c & x & Block{3-1}{text{Side Title}} 
d & e & f & y 
g & h & i & z   
CodeAfter SubMatrix[{3-1}{5-3}]
end{NiceMatrix}$
end{document}

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