equationsnumbering
I would like to quote a part of a paper and would like to keep the same numbering of equations. For example, suppose in a paper, the equation appears
\begin{equation}
1 + 1 = 2
\end{equation}
And appears numbered as (5) in the paper, and not (1) which would appear when I type it out in LaTeX. I would like to give a direct quote of the paper, including the equation number. Is there any way to do this?
This can go wrong if the figure floats after LaTeX has typeset other numbered equations, but here it is anyway:
\documentclass{scrreprt}
\usepackage{amsmath, amssymb,siunitx}
\begin{document}
\begin{equation}
\label{eq:periodischefunktion}
f(t)=f(t+T),
\end{equation}
\begin{figure}[ht]
\renewcommand*\figurename{Gleichung}
\makeatletter
\let\c@figure\c@equation
\makeatother
\[
\begin{vmatrix}
c_{F_x\vec{x}} & c_{F_y\vec{x}} & c_{F_z\vec{x}}\\
c_{F_x\vec{y}} & c_{F_y\vec{y}} & c_{F_z\vec{y}}\\
c_{F_x\vec{z}} & c_{F_y\vec{z}} & c_{F_z\vec{z}}\\
\end{vmatrix}_{\mathrm{stat}} =
\begin{vmatrix}
410,6 & - & -\\
- & 318,7 & -\\
- & - & -\\
\end{vmatrix}
\si[per-mode=fraction]{\newton\per\milli\meter}
\]
\caption{Steifigkeitsmatrix bei Auskragung $A=\SI{0}{\milli\meter}$}
\label{eq:steifmatrix0}
\end{figure}
\begin{figure}[ht]
Normal
\caption{Normal figure}
\end{figure}
Some reference to \ref{eq:steifmatrix0}.
\end{document}
The trick is to make (locally) the caption in the figure environment use equation.
The presence of the full stop is not relevant at all. You get exactly the same effect with
\begin{equation}
\centerline{$a=b$}
\end{equation}
and
\begin{equation}
\centerline{$a=b$}
\end{equation}
The fact is that the input is wrong to begin with: \centerline is a Plain TeX macro and should not be used in LaTeX, unless very special effects are needed.
An equation environment already centers the math material without any further effort. So your input should be
\documentclass{article} % this class just for producing the example
\usepackage{amsmath} % for math typesetting
\begin{document}
\begin{equation}
\label{ix}
I_{\textup{aligned}} = I - I_{\textup{rot}}.
\end{equation}
\end{document}
Note that blank lines are not allowed inside equation and that the textual subscript should be in the upright font.
Best Answer
You can set the number of the equations yourself with
\tagand this will keep your equation numbers other than the tagged value the same. This looks odd though and perhaps isn't what you are looking for?