Alignedat environment - remove extra blank space

Question

I'm dealing with a math system and the code is the following:

\documentclass{report}
\usepackage{mathtools}
\begin{document}
\begin{spreadlines}{1.ex}
        \begin{equation}
        \chi_{_\mathrm{f}}=\mu^T
        \left\{
            \begin{alignedat}{2}
                (R_{x_\mathrm{f}} - R_{x_\mathrm{fs}}) = 0 \;\xrightarrow{R_{x_\mathrm{fs}} =0} \; (R_{x_\mathrm{f}} = 0)\\
                (R_{y_\mathrm{f}} - R_{y_\mathrm{fs}}) = 0 \;\xrightarrow{R_{y_\mathrm{fs}}=0} \; (R_{y_\mathrm{f}} = 0)\\
                (R_{z_\mathrm{f}} - R_{z_\mathrm{fs}}) = 0 \;\xrightarrow{R_{z_\mathrm{fs}}=0} \; (R_{z_\mathrm{f}} = 0)\\
                (V_{x_\mathrm{f}} - V_{x_\mathrm{fs}}) = 0 \;\xrightarrow{V_{x_\mathrm{fs}}=0} \; (V_{x_\mathrm{f}} = 0)\\
                (V_{y_\mathrm{f}} - V_{y_\mathrm{fs}}) = 0 \;\xrightarrow{V_{y_\mathrm{fs}}=0} \; (V_{y_\mathrm{f}} = 0)\\
                (V_{z_\mathrm{f}} - V_{z_\mathrm{fs}}) = 0 \;\xrightarrow{V_{z_\mathrm{fs}}=0} \; (V_{z_\mathrm{f}} = 0)\\ 
                m_f \text{free}\\
            \end{alignedat}
        \right.
        \end{equation}
        \end{spreadlines}
\end{document}

The output is the following:

1. How could I remove the extra space that the code generate in the final line within the system? I have no clue why the last row starts there. It would be nice having it aligned on the left side like all the other rows or centered at least.

2. How can I correctly outdistance "m_f" and "free" each other?

Thank you!

Answer 1

I think gathered is preferable in this case to alignedat since there are no alignments per se. Then, I added a space at the beginning of \text{ free} to introduce the desired space. Finally, I led with an \mkern8mu and trailed with an \hfill on the last line to achieve left alignment of the final line (without them, the text is centered).

\documentclass{report}
\usepackage{mathtools}
\begin{document}
\begin{spreadlines}{1.ex}
        \begin{equation}
        \chi_{_\mathrm{f}}=\mu^T
        \left\{
            \begin{gathered}
                (R_{x_\mathrm{f}} - R_{x_\mathrm{fs}}) = 0 \;\xrightarrow{R_{x_\mathrm{fs}} =0} \; (R_{x_\mathrm{f}} = 0)\\
                (R_{y_\mathrm{f}} - R_{y_\mathrm{fs}}) = 0 \;\xrightarrow{R_{y_\mathrm{fs}}=0} \; (R_{y_\mathrm{f}} = 0)\\
                (R_{z_\mathrm{f}} - R_{z_\mathrm{fs}}) = 0 \;\xrightarrow{R_{z_\mathrm{fs}}=0} \; (R_{z_\mathrm{f}} = 0)\\
                (V_{x_\mathrm{f}} - V_{x_\mathrm{fs}}) = 0 \;\xrightarrow{V_{x_\mathrm{fs}}=0} \; (V_{x_\mathrm{f}} = 0)\\
                (V_{y_\mathrm{f}} - V_{y_\mathrm{fs}}) = 0 \;\xrightarrow{V_{y_\mathrm{fs}}=0} \; (V_{y_\mathrm{f}} = 0)\\
                (V_{z_\mathrm{f}} - V_{z_\mathrm{fs}}) = 0 \;\xrightarrow{V_{z_\mathrm{fs}}=0} \; (V_{z_\mathrm{f}} = 0)\\ 
                \mkern8mu m_f \text{ free}\hfill
            \end{gathered}
        \right.
        \end{equation}
        \end{spreadlines}
\end{document}

Answer 2

Three possibilities. The various parts have different widths, so it's difficult to get sensible alignments, so I recommend the last one.

\documentclass{report}
\usepackage{mathtools}

\begin{document}

\begin{equation}
\chi_{_\mathrm{f}}=\mu^T
\left\{
  \begin{alignedat}{4}
  &(R_{x_\mathrm{f}} - R_{x_\mathrm{fs}}) &&= 0
    &&\xrightarrow{R_{x_\mathrm{fs}} =0} (R_{x_\mathrm{f}} = 0)\\
  &(R_{y_\mathrm{f}} - R_{y_\mathrm{fs}}) &&= 0
    &&\xrightarrow{R_{y_\mathrm{fs}}=0} (R_{y_\mathrm{f}} = 0)\\
  &(R_{z_\mathrm{f}} - R_{z_\mathrm{fs}}) &&= 0
    &&\xrightarrow{R_{z_\mathrm{fs}}=0} (R_{z_\mathrm{f}} = 0)\\
  &(V_{x_\mathrm{f}} - V_{x_\mathrm{fs}}) &&= 0
    &&\xrightarrow{V_{x_\mathrm{fs}}=0} (V_{x_\mathrm{f}} = 0)\\
  &(V_{y_\mathrm{f}} - V_{y_\mathrm{fs}}) &&= 0
    &&\xrightarrow{V_{y_\mathrm{fs}}=0} (V_{y_\mathrm{f}} = 0)\\
  &(V_{z_\mathrm{f}} - V_{z_\mathrm{fs}}) &&= 0
    &&\xrightarrow{V_{z_\mathrm{fs}}=0} (V_{z_\mathrm{f}} = 0)\\[1ex]
  &\text{$m_{\mathrm{f}}$ free}
  \end{alignedat}
\right.
\end{equation}

\begin{equation}
\chi_{_\mathrm{f}}=\mu^T
\left\{
  \begin{alignedat}{3}
  &(R_{x_\mathrm{f}} - R_{x_\mathrm{fs}}) = 0
    &&\xrightarrow{R_{x_\mathrm{fs}} =0} (R_{x_\mathrm{f}} &= 0)\\
  &(R_{y_\mathrm{f}} - R_{y_\mathrm{fs}}) = 0
    &&\xrightarrow{R_{y_\mathrm{fs}}=0} (R_{y_\mathrm{f}} &= 0)\\
  &(R_{z_\mathrm{f}} - R_{z_\mathrm{fs}}) = 0
    &&\xrightarrow{R_{z_\mathrm{fs}}=0} (R_{z_\mathrm{f}} &= 0)\\
  &(V_{x_\mathrm{f}} - V_{x_\mathrm{fs}}) = 0
    &&\xrightarrow{V_{x_\mathrm{fs}}=0} (V_{x_\mathrm{f}} &= 0)\\
  &(V_{y_\mathrm{f}} - V_{y_\mathrm{fs}}) = 0
    &&\xrightarrow{V_{y_\mathrm{fs}}=0} (V_{y_\mathrm{f}} &= 0)\\
  &(V_{z_\mathrm{f}} - V_{z_\mathrm{fs}}) = 0
    &&\xrightarrow{V_{z_\mathrm{fs}}=0} (V_{z_\mathrm{f}} &= 0)\\[1ex]
  &\text{$m_{\mathrm{f}}$ free}
  \end{alignedat}
\right.
\end{equation}

\begin{equation}
\chi_{_\mathrm{f}}=\mu^T
\left\{
  \begin{alignedat}{1}
  &(R_{x_\mathrm{f}} - R_{x_\mathrm{fs}}) = 0
    \xrightarrow{R_{x_\mathrm{fs}} =0} (R_{x_\mathrm{f}} = 0)\\
  &(R_{y_\mathrm{f}} - R_{y_\mathrm{fs}}) = 0
    \xrightarrow{R_{y_\mathrm{fs}}=0} (R_{y_\mathrm{f}} = 0)\\
  &(R_{z_\mathrm{f}} - R_{z_\mathrm{fs}}) = 0
    \xrightarrow{R_{z_\mathrm{fs}}=0} (R_{z_\mathrm{f}} = 0)\\
  &(V_{x_\mathrm{f}} - V_{x_\mathrm{fs}}) = 0
    \xrightarrow{V_{x_\mathrm{fs}}=0} (V_{x_\mathrm{f}} = 0)\\
  &(V_{y_\mathrm{f}} - V_{y_\mathrm{fs}}) = 0
    \xrightarrow{V_{y_\mathrm{fs}}=0} (V_{y_\mathrm{f}} = 0)\\
  &(V_{z_\mathrm{f}} - V_{z_\mathrm{fs}}) = 0
    \xrightarrow{V_{z_\mathrm{fs}}=0} (V_{z_\mathrm{f}} = 0)\\[1ex]
  &\text{$m_{\mathrm{f}}$ free}
  \end{alignedat}
\right.
\end{equation}

\end{document}

Answer 3

You appear to be missing the entire point of using an alignedat environment: It exists so you don't have to engage in (presumably tedious) visual formatting via spacing directives such as \;. But if you don't provide any & alignment markers, there's little or no reason for using alignedat (or align, aligned, flalign, etc.) to begin with.

Anyway, I'd get rid of the \; spacers and insert well-placed alignment markers instead.

\documentclass{report}
\usepackage{mathtools}
\newcommand\fs{\mathrm{fs}} % handy shortcut macro

\begin{document}
\begin{spreadlines}{1ex}
\begin{equation}
\chi^{}_{\mathrm{f}}=\mu^T
\left\{
\begin{alignedat}{3}
   (R_{x_\mathrm{f}} - R_{x_{\fs}}) &= 0 \xrightarrow{R_{x_{\fs}}=0}  &&(R_{x_\mathrm{f}} &= 0)\\
   (R_{y_\mathrm{f}} - R_{y_{\fs}}) &= 0 \xrightarrow{R_{y_{\fs}}=0}  &&(R_{y_\mathrm{f}} &= 0)\\
   (R_{z_\mathrm{f}} - R_{z_{\fs}}) &= 0 \xrightarrow{R_{z_{\fs}}=0}  &&(R_{z_\mathrm{f}} &= 0)\\
   (V_{x_\mathrm{f}} - V_{x_{\fs}}) &= 0 \xrightarrow{V_{x_{\fs}}=0}  &&(V_{x_\mathrm{f}} &= 0)\\
   (V_{y_\mathrm{f}} - V_{y_{\fs}}) &= 0 \xrightarrow{V_{y_{\fs}}=0}  &&(V_{y_\mathrm{f}} &= 0)\\
   (V_{z_\mathrm{f}} - V_{z_{\fs}}) &= 0 \xrightarrow{V_{z_{\fs}}=0}  &&(V_{z_\mathrm{f}} &= 0)\\ 
   m_{\mathrm{f}} \text{ free}\qquad\\
\end{alignedat}
\right.
\end{equation}
\end{spreadlines}
\end{document}