mjhjmtu

I have some split equations with intertext, like this:

documentclassarticle
usepackageamsmath

begindocument
beginequation
beginsplit
 y_j &= frac135left(-3y_j-2+12y_j-1+17y_j+12y_j+1-3y_j+2right),\
 intertextwhere
 C_-2&=-frac335,C_1=frac1235,textetc.
endsplit
endequation
enddocument

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.

I'd propose to use align here.

documentclass[fleqn]article
usepackageamsmath

begindocument
beginalign
 y_j &= frac135left(-3y_j-2+12y_j-1+17y_j+12y_j+1-3y_j+2right),\
 intertextwhere
 C_-2&=-frac335,quad C_1=frac1235, quadtextetc.notag
endalign
enddocument

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.

documentclassarticle
usepackageamsmath

begindocument

beginequation
 y_j = frac135(-3y_j-2+12y_j-1+17y_j+12y_j+1-3y_j+2),
endequation
where
beginequation*
C_-2=-frac335,quad C_1=frac1235,quadtextetc.
endequation*

enddocument

If you really want to do the alignment, use shortintertext from mathtools:

documentclassarticle
usepackageamsmath,mathtools

begindocument

beginalign
 y_j &= frac135(-3y_j-2+12y_j-1+17y_j+12y_j+1-3y_j+2), \
shortintertextwhere
C_-2&=-frac335,quad C_1=frac1235,quadtextetc. notag
endalign

enddocument