Background
 Mathematics Stack Exchange use Markdown and MathJax to typeset math expressions.
 I use GNU Octave to efficiently perform (matrix) calculations for a quick and correct response on Mathematics Stack Exchange.
Problem
Recently, I encountered a linear algebra problem on Mathematics Stack Exchange.
For any given matrix $A$ in Octave,
A = [1 2 2; 2 3 4; 4 4 2]
A =
1 2 2
2 3 4
4 4 2
how can one generate its $\rm \LaTeX$ code
1


so that one gets
Solution
I searched “octave to latex matrices” and I found this answer quite useful. I issued the first command to see the result.
strrep(strrep(mat2str(A),",","&"),";","\\\\\n")(2:end1)
ans = 1 2 2\\
2 3 4\\
4 4 2
I suspected that it didn’t work. I posted it as a comment and
verified that I was right. To fix this, I extracted the function
mat2str(A)
in the middle of this command to see the results. From
its result (ans = [1 2 2;2 3 4;4 4 2]
), I realised that strrep
standed for “string replace”. Then, I changed the doublequoted comma
in the second argument of function strrep
to a doublequoted
whitespace character, and got the anticipated result.
strcat("\\begin{bmatrix}\n",strrep(strrep(mat2str(A)," ","&"), ...
";","\\\\\n")(2:end1),"\n\\end{bmatrix}\n")
ans = \begin{bmatrix}
1&2&2\\
2&3&4\\
4&4&2
\end{bmatrix}
Inadequacies
I don’t know how to do this for matrices with fractions. I think I can work it out by searching and testing in several hours, but I don’t have the time to do so.
Lessons learnt
Math
I revised some definitions in linear algebra.
 A matrix $U$ is unitary iff $UU^\star = U^\star U = I$.
 A matrix $N$ is normal iff $NN^\star = N^\star N$.
GNU Octave
 The function
strrep(str,"foo","bar")
replaces all instances offoo
instr
withbar
. It can be used in a nested manner for multiple replacements.  The function
strcat(str1,str2,...)
concatenates the strings inside.
Grep
When I was writing this article, I wanted to search for “octave”
(with the square brackets “[]”) with grep
inside Vim, but I got
over 1270 results. I tried adding single/double quotes and escaping
the square brackets with a backslash, but I faied again. Finally, I
googled “grep escape character” for a solution. Since then, I know
that I should add the F
flag to grep
to fix the
string.