s=String.raw`\[
A= \begin{pmatrix}
a_{11}^2 & a_{12}^ 2 &a_{13}^2 \\
0 & a_{22} & a_{23} \\
0 & 0 &a_{23} \\
0 & 0 &a_{33}
\end{pmatrix}
\]`;
l=s.length;
for(i=0;i<l;i++){
console.log(i);
console.log(s[i]);
console.log(s[i]==' ');
}