Q: How to have equation number at top with intertext in split environment I have some split equations with intertext, like this:
\documentclass{article}
\usepackage{amsmath}

\begin{document}
\begin{equation}
\begin{split}
    y_j &= \frac{1}{35}\left(-3y_{j-2}+12y_{j-1}+17y_j+12y_{j+1}-3y_{j+2}\right),\\
    \intertext{where}
    C_{-2}&=-\frac{3}{35},C_1=\frac{12}{35},\text{etc.}
\end{split}
\end{equation}
\end{document}

And I need the equation number to display vertically aligned with the top line, however my in the current output the equation number is at the bottom:

How would I go about this?
Thanks in advance.

A: I'd propose to use align here.
\documentclass[fleqn]{article}
\usepackage{amsmath}

\begin{document}
\begin{align}
    y_j &= \frac{1}{35}\left(-3y_{j-2}+12y_{j-1}+17y_j+12y_{j+1}-3y_{j+2}\right),\\
    \intertext{where}
    C_{-2}&=-\frac{3}{35},\quad C_1=\frac{12}{35}, \quad\text{etc.}\notag
\end{align}
\end{document}



A: By default, the equation number is centered with respect to a split; if the tbtags option is passed to amsmath, the number will be aligned with the top line (if on the left) or with the bottom line (if on the right).
Therefore split is the wrong tool, not to mention that \intertext makes a line as wide as \columnwidth, so the whole split appears to be too wide for the equation number to fit, which is the reason it is lowered below the second line.
You could use align, with \notag in the second line, but I see no reason for aligning unrelated = symbols.
\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{equation}
 y_j = \frac{1}{35}(-3y_{j-2}+12y_{j-1}+17y_j+12y_{j+1}-3y_{j+2}),
\end{equation}
where
\begin{equation*}
C_{-2}=-\frac{3}{35},\quad C_1=\frac{12}{35},\quad\text{etc.}
\end{equation*}

\end{document}


If you really want to do the alignment, use \shortintertext from mathtools:
\documentclass{article}
\usepackage{amsmath,mathtools}

\begin{document}

\begin{align}
 y_j &= \frac{1}{35}(-3y_{j-2}+12y_{j-1}+17y_j+12y_{j+1}-3y_{j+2}), \\
\shortintertext{where}
C_{-2}&=-\frac{3}{35},\quad C_1=\frac{12}{35},\quad\text{etc.} \notag
\end{align}

\end{document}


