Creating a multiline equation

Question

I am really struggling to create a multi line equation that incorporates both a matrix and a single equation that lines up the equals signs such as the one below:

So far have done the following:

\begin{equation*}
    M =  U\Sigma V^{*}
\end{equation*}
\begin{equation}        
     = \textbf{U}\left[ \begin{array}{cccc} 
     \sigma_{1} & 0 & \ldots & 0\\
     0 & \sigma_{2} & \ldots & 0\\
     \vdots & \vdots & \ddots & \vdots\\
     0 & 0 & \ldots & \sigma_{m}\\   
     \end{array} \right]\textbf{V*}
\end{equation}

Answer 1

You could use your code inside the align environment:

\documentclass{article}

\usepackage{amsmath}

\begin{document}

\begin{align}
\mathbf{M} &= \mathbf{U}\Sigma \mathbf{V}^{*} \nonumber\\
           &= \mathbf{U}\left[\begin{array}{cccc} 
              \sigma_{1} & 0 & \ldots & 0\\
              0 & \sigma_{2} & \ldots & 0\\
              \vdots & \vdots & \ddots & \vdots\\
              0 & 0 & \ldots & \sigma_{m}\\   
              \end{array} \right]\textbf{V*}
\end{align}

\end{document}