Alinhe múltiplas equações com múltiplas expressões

Question

Aqui está o que fiz até agora. Quero que o espaço do meio reduza um pouco.

\documentclass[10pt]{article}
\usepackage{amsmath, amsthm, amssymb}
\begin{document}
\begin{align}
\Vert\mathbf{R}\Vert_F^2  & \le  \Vert\mathbf{R}\Vert_F^2 +\lambda\Vert 
\mathbf{B}^{'}\Vert_F^2-\sum_{k=1}^{m}\Vert \mathbf{B}^{'}\mathbf{A}\Vert_F^2 & & = 
\Vert\mathbf{R}\Vert_F^2 +\lambda\Vert \mathbf{B}^{'}\Vert_F^2-\sum_{k=1}^{m}\Vert
\mathbf{b}_k\mathbf{a}_{[k]}\Vert_F^2 \nonumber \\
& = \Vert\mathbf{R}\Vert_F^2 +\lambda\sum_{k=1}^{m}\Vert \mathbf{b}_k\Vert_2^2 -
\sum_{k=1}^{m}\Vert \mathbf{W}_k\Vert_F^2 & &= \Vert\mathbf{R}\Vert_F^2 -
\sum_{k=1}^{m}\Vert    \mathbf{b}_k\Vert_2^2\Vert\mathbf{a}_{[k]}\Vert_2^2 +\lambda m 
\label{eq6} 
\end{align}
\end{document}    

Answer 1

Você pode adicionar algum espaço negativo, por exemplo, \hspace*{-1em}antes do último=

MWE

\documentclass[10pt]{article}
\usepackage{amsmath, amsthm, amssymb}
\begin{document}
\begin{align}
\Vert\mathbf{R}\Vert_F^2  & \le  \Vert\mathbf{R}\Vert_F^2 +\lambda\Vert
\mathbf{B}^{'}\Vert_F^2-\sum_{k=1}^{m}\Vert \mathbf{B}^{'}\mathbf{A}\Vert_F^2 & \hspace*{-1em} & =
\Vert\mathbf{R}\Vert_F^2 +\lambda\Vert \mathbf{B}^{'}\Vert_F^2-\sum_{k=1}^{m}\Vert
\mathbf{b}_k\mathbf{a}_{[k]}\Vert_F^2 \nonumber \\
& = \Vert\mathbf{R}\Vert_F^2 +\lambda\sum_{k=1}^{m}\Vert \mathbf{b}_k\Vert_2^2 -
\sum_{k=1}^{m}\Vert \mathbf{W}_k\Vert_F^2 & \hspace*{-1em} &= \Vert\mathbf{R}\Vert_F^2 -
\sum_{k=1}^{m}\Vert    \mathbf{b}_k\Vert_2^2\Vert\mathbf{a}_{[k]}\Vert_2^2 +\lambda m
\label{eq6}
\end{align}
\end{document}  

Saída

De qualquer forma, como você pode ver, a equação ainda é muito longa para caber nas retas. Eu sugiro inserir mais algumas pausas:

\documentclass[10pt]{article}
\usepackage{amsmath, amsthm, amssymb}
\begin{document}
\begin{equation}
\begin{aligned}
\Vert\mathbf{R}\Vert_F^2  & \le  \Vert\mathbf{R}\Vert_F^2 +\lambda\Vert
\mathbf{B}^{'}\Vert_F^2-\sum_{k=1}^{m}\Vert \mathbf{B}^{'}\mathbf{A}\Vert_F^2 \\
& = \Vert\mathbf{R}\Vert_F^2 +\lambda\Vert \mathbf{B}^{'}\Vert_F^2-\sum_{k=1}^{m}\Vert
\mathbf{b}_k\mathbf{a}_{[k]}\Vert_F^2 \\
& = \Vert\mathbf{R}\Vert_F^2 +\lambda\sum_{k=1}^{m}\Vert \mathbf{b}_k\Vert_2^2 -
\sum_{k=1}^{m}\Vert \mathbf{W}_k\Vert_F^2 \\
& = \Vert\mathbf{R}\Vert_F^2 -\sum_{k=1}^{m}\Vert
\mathbf{b}_k\Vert_2^2\Vert\mathbf{a}_{[k]}\Vert_2^2 +\lambda m
\label{eq6}
\end{aligned}
\end{equation}
\end{document} 

Saída

Observe o uso de equatione alignedem vez de alignpara evitar o uso de \nonumber.

Answer 2

Aqui está como eu faria isso:

\documentclass{article}

\usepackage[margin = 4cm]{geometry}
\usepackage{mathtools}

\newcommand*\Vector[1]{\mathbf{#1}}
\DeclarePairedDelimiter{\norm}{\lVert}{\rVert}
\DeclarePairedDelimiter{\something}{\lbrack}{\rbrack}

\begin{document}

\noindent Either
\begin{alignat}{2}
  \norm{\Vector{R}}_{F}^{2}
  &\le \norm{\Vector{R}}_{F}^{2} + \lambda \norm{\Vector{B}'}_{F}^{2}
       -\sum_{k = 1}^{m} \norm{\Vector{B}'{\mkern -2mu}\Vector{A}}_{F}^{2}
  &&= \norm{\Vector{R}}_{F}^{2} + \lambda \norm{\Vector{B}'}_{F}^{2}
      -\sum_{k = 1}^{m} \norm{\Vector{b}_{k}\Vector{a}_{\something{k}}}_{F}^{2} \nonumber \\
  &= \norm{\Vector{R}}_{F}^{2} + \lambda \sum_{k = 1}^{m} \norm{\Vector{b}_{k}}_{2}^{2}
     -\sum_{k = 1}^{m} \norm{\Vector{W}_{k}}_{F}^{2}
  &&= \norm{\Vector{R}}_{F}^{2} - \sum_{k = 1}^{m} \norm{\Vector{b}_{k}}_{2}^{2}
      \,\norm{\Vector{a}_{\something{k}}}_{2}^{2} + \lambda m 
\end{alignat}
or
\begin{align}
  \norm{\Vector{R}}_{F}^{2}
  &\le \norm{\Vector{R}}_{F}^{2} + \lambda \norm{\Vector{B}'}_{F}^{2}
       -\sum_{k = 1}^{m} \norm{\Vector{B}'{\mkern -2mu}\Vector{A}}_{F}^{2} \nonumber \\
  &= \norm{\Vector{R}}_{F}^{2} + \lambda \norm{\Vector{B}'}_{F}^{2}
     -\sum_{k = 1}^{m} \norm{\Vector{b}_{k}\Vector{a}_{\something{k}}}_{F}^{2} \nonumber \\
  &= \norm{\Vector{R}}_{F}^{2} + \lambda \sum_{k = 1}^{m} \norm{\Vector{b}_{k}}_{2}^{2}
     -\sum_{k = 1}^{m} \norm{\Vector{W}_{k}}_{F}^{2} \nonumber \\
  &= \norm{\Vector{R}}_{F}^{2} - \sum_{k = 1}^{m} \norm{\Vector{b}_{k}}_{2}^{2}
     \,\norm{\Vector{a}_{\something{k}}}_{2}^{2} + \lambda m 
\end{align}

\end{document}

Observe o uso de \DeclarePairedDelimiterfrom themathtoolspacote.