Matrix Equation Text over text in braces

Question

Hi, how can I write this equation in Latex?

Answer 1

Never seen this kind of formula, so I don't know if this exactly what you want to achieve:

\documentclass{article}
\usepackage{amsmath}
\newcommand{\mymatr}[2]{\big[\overset{\scriptscriptstyle #1}{#2}\big]}
\newcommand{\myind}[1]{\raisebox{1pt}{$\scriptscriptstyle #1$}}
\begin{document}
    \[
    \mymatr{N}{X}\myind{M}=
        \myind{M}\mymatr{M}{U}\mymatr{N}{S}\myind{M}
        \mymatr{N}{V}^{T}\myind{N}
    \]
    or
    \[
    \mymatr{N}{X}\myind{M}=
    \myind{M}\mymatr{M}{U}\mymatr{N}{S}\myind{M}
    \mymatr{N}{V}^{\scriptscriptstyle T}\myind{N}
    \]
\end{document}