Centered equation with raggeredleft text

Question

I'd like to replicate the line of the framed equation (5.11): (ignore the text above):

that is, "place the word 'or' (or another word) on the same line as -- but maximally separated from -- the framed equation (5.11)".

For example, instead of having this:

I'd like to have:

EDIT

I tried using \shortintertext command from mathtools package but that's not what I'm looking for (I appreciate the help though!!)

Answer 1

"The customer is always right" is an old truism. However, this rule does have some exceptions.

The OP's request is just such case: By placing the word "or" on the same line as -- but maximally separated from -- the framed equation (5.11), the word "or" actually becomes nearly invisible and unnoticeable. Presumably, that is not the OP's intention.

I suggest that the OP load the mathtools package, employ an align environment to typeset to equations, and place the word "or" in a \shortintertext wrapper. That way, text and math are visually separated and remain equally visible.

\documentclass{article} % or some other suitable document class
\usepackage{mathtools}  % for \shortintertext and \Aboxed macros
\usepackage{lipsum} % filler text
\usepackage{newtxtext,newtxmath} % optional: Times Roman text and math fonts
\counterwithin{equation}{section} % just for this example

\begin{document}
\setcounter{section}{5} % just for this example
\setcounter{equation}{10}

\noindent
\lipsum[1][1-3] % filler text
\begin{align}
\ln P &= -\gamma\ln V + \ln\text{const.} \notag \\
\shortintertext{or}
\Aboxed{PV^{\gamma} &= \text{const.}}
\end{align}
This equation of state holds for all equilibrium states through which the ideal \dots
\end{document}

---

Addendum to address the OP's follow-up comment: I suppose the OP's desired layout could be achieved by using (abusing!) an flalign environment; see the upper part of the screenshot below.

I can only hope that the OP will take @gildux's earlier comment

I thought the [word] "or" was part of the equation (or a cell of an equation array or something like that). The image looks strange...

to heart and decide against pursuing the flalign approach after all. Yes, the flalign "saves" a bit more than 1\baselineskip in vertical space expended on the document -- at the cost of producing something that's confusing or misleading (or both!). In short, the OP's desired layout is a sadly-excellent illustration of the old-time expression "penny-wise but pound-foolish". :-)

\documentclass{article}
\usepackage{mathtools}
\usepackage{newtxtext,newtxmath} % optional
\begin{document}
\hrule
\begin{flalign}
          && \ln P &= -\gamma\ln V + \ln\text{const.} & \notag \\
\text{or} && \Aboxed{PV^{\gamma} &= \text{const.}}    &
\end{flalign}
\hrule
\smallskip
\noindent vs.
\smallskip
\hrule
\begin{align}
\ln P &= -\gamma\ln V + \ln\text{const.} \notag \\
\shortintertext{or}
\Aboxed{PV^{\gamma} &= \text{const.}}
\end{align}
\hrule
\end{document}

Answer 2

You can center both equations, with some pain.

\documentclass{article}
\usepackage{amsmath}
\usepackage{newtxtext,newtxmath}

\usepackage{lipsum} % filler text

\counterwithin{equation}{section} % just for this example

\begin{document}

\setcounter{section}{5} % just for this example
\setcounter{equation}{10}

\noindent
\lipsum[1][1-3] % filler text
\begin{equation*}
\ln P = -\gamma\ln V + \ln\text{const.}
\end{equation*}
\noindent
\begin{equation}
\hspace{-0.5em}\makebox[0pt][l]{or}
\settowidth{\dimen0}{\theequation}%
\hspace{\dimen0}\quad
\hspace{1000pt minus 1fil}
\boxed{PV^{\gamma} = \text{const.}}
\hspace{1000pt minus 1fil}
\end{equation}
This equation of state holds for all equilibrium states through which the ideal

\end{document}

However, I'd not pursue this strategy, because “or” doesn't belong to the equation.

\documentclass{article}
\usepackage{amsmath,mathtools}
\usepackage{newtxtext,newtxmath}

\usepackage{lipsum} % filler text

\counterwithin{equation}{section} % just for this example

\begin{document}

\setcounter{section}{5} % just for this example
\setcounter{equation}{10}

\noindent
\lipsum[1][1-3] % filler text
\begin{gather}
\ln P = -\gamma\ln V + \ln\text{const.}\notag \\
\shortintertext{or, in different form,}
\boxed{PV^{\gamma} = \text{const.}}
\end{gather}
This equation of state holds for all equilibrium states through which the ideal

\end{document}