Ttgjyuk

I understand how to align multiple equations, but how can I do this if I want to also have text over the equalities. For example:

It bugs me that the equal signs are no longer aligned. Here is my LaTeX:

$$
beginalign
p(textbfx mid mathcalD, alpha)
&= int p(textbfx mid boldsymboltheta) p(boldsymboltheta mid mathcalD, alpha) textd boldsymboltheta
\
&stackreltextEq 4= int p(textbfx mid boldsymboltheta) p(boldsymboltheta mid alpha') textd boldsymboltheta
\
&= p(textbfx mid alpha'). tag5
endalign
$$

Is there a solution to this?

Here I use mathclap to insure that the overstack takes up zero horizontal space.

Also, change the textbf instances to mathbf (thanks, Mico).

Finally, ditch the $$ delimiters.

documentclassarticle
usepackagemathtools
begindocument

beginalign
p(mathbfx mid mathcalD, alpha)
&= int p(mathbfx mid boldsymboltheta) p(boldsymboltheta mid mathcalD, alpha) textd boldsymboltheta
\
&stackrelmathclaptextEq 4= int p(mathbfx mid boldsymboltheta) p(boldsymboltheta mid alpha') textd boldsymboltheta
\
&= p(mathbfx mid alpha'). tag5
endalign


enddocument

A simple makebox[0pt]... will solve the probl.

Unrelated: do not nest align inside $$ ... $$ – and don't use the plain TeX construct ˆˆ ... $$ as it will yield incorrect spacing in LaTeX.

documentclassarticle
usepackageamsmath

begindocument

beginalign
p(textbfx mid mathcalD, alpha)
&= int p(textbfx mid boldsymboltheta) p(boldsymboltheta mid mathcalD, alpha) textd boldsymboltheta
\
&stackreltextmakebox[0pt]Eq 4= int p(textbfx mid boldsymboltheta) p(boldsymboltheta mid alpha') textd boldsymboltheta
\
&= p(textbfx mid alpha'). tag5
endalign

enddocument