[Tex/LaTex] \hfill in math mode redux

horizontal alignmentmath-mode

This is a followup to this thread. I basically followed the construction offered by @egreg. The following construction throws an error when I have a & b in the line with \pushright. If I omit the b the code runs. Is there a way that I can use \pushright and have symbols to the right of the & sign?

\documentclass{article}
\usepackage{amsmath}
\makeatletter
\newcommand{\pushright}[1]{\ifmeasuring@#1\else\omit$\displaystyle#1$\ignorespaces\fi}
\makeatother

\begin{document}
\begin{align}
    a  &   b  \pushright{\hfill\text{(foo)}}
\end{align}
\end{document}

Ultimately, what I want to do is have lines like:

\begin{align}
    x_{t+1} = & x_t + f(x_t) - c_t  \pushright{\hfill\text{(eq of motion)}} \\
    x_0     = & \bar{x}       \pushright{\hfill\text{(initial condition)}}
\end{align}

and have the phrases eq of motion and initial condition right aligned just to the left of the equation numbers. Thanks!

Best Answer

Like that?

\begin{align}
    x_{t+1} = & x_t + f(x_t) - c_t  & \pushright{\hfill\text{(eq of motion)}} \\
    x_0     = & \bar{x}       & \pushright{\hfill\text{(initial condition)}}
\end{align}

Related Solutions

[Tex/LaTex] \hfill in math mode

You can do it, but not with \hfill, because of how align works. Here's a way:

\documentclass{article}
\usepackage{amsmath}

\makeatletter
\newcommand{\pushright}[1]{\ifmeasuring@#1\else\omit\hfill$\displaystyle#1$\fi\ignorespaces}
\newcommand{\pushleft}[1]{\ifmeasuring@#1\else\omit$\displaystyle#1$\hfill\fi\ignorespaces}
\makeatother

\begin{document}
\begin{align*}
    a + b + c &= a + b + c + d + e + f + g + h + i \\
    & \pushright{\text{(foo)}}
\end{align*}


\begin{align*}
    a + b + c + d + e + f + g + h + i &= a + b + c \\
    \pushleft{\text{(foo)}} &
\end{align*}

\end{document}

enter image description here

A slightly different implementation allows you to use \hfill where you want:

\documentclass{article}
\usepackage{amsmath}

\makeatletter
\newcommand{\specialcell}[1]{\ifmeasuring@#1\else\omit$\displaystyle#1$\ignorespaces\fi}
\makeatother

\begin{document}
\begin{align*}
    a + b + c &= a + b + c + d + e + f + g + h + i \\
    & \specialcell{\hfill\text{(foo)}}
\end{align*}


\begin{align*}
    a + b + c + d + e + f + g + h + i &= a + b + c \\
    \specialcell{\text{(foo)}\hfill} \\
    \specialcell{\hfill\text{(foo)}\hfill}
\end{align*}

\end{document}

I'd recommend against using the simple \omit.

enter image description here

[Tex/LaTex] `\hfill`-like spacing in math mode without using `align`

You can force things to stretch by giving them a large natural width and allowing them to shrink, rather than \hfill which has a natural width of 0pt.

$$a\hskip \textwidth minus \textwidth b$$

produces

enter image description here

But a CD package is almost certainly making a box anyway so placing them inside a display math environment probably doesn't achieve much, however if you mean what I think you mean then putting shrinkable glue between two boxes will force them apart as shown here.

Best Answer

Related Solutions

[Tex/LaTex] \hfill in math mode

[Tex/LaTex] `\hfill`-like spacing in math mode without using `align`

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