# How to position “=” mid-line inside a '\raisebox' and then align using &= with expression below?

In order to get a full stop at the bottom, rather than mid-line, after an aligned matrix expression, I have raised the expression using a raisebox, and adjusted space using vspace'. This is now causing further problems. The expression contains an "=", but this is now going to the bottom rather than staying mid-line. How do I keep it mid-line? Also, how do I now align the expression with an expression below which is not in a raisebox?

It might be easiest if I show what I had before using the raisebox. I want to keep this the same, except with the full stop at the bottom:

\begin{align}
\begin{pmatrix} a\\b \end{pmatrix} &= \begin{pmatrix} c\\d \end{pmatrix}.\\
\intertext{Now}
\begin{pmatrix} e\\f \end{pmatrix}&= \begin{pmatrix} g\\h \end{pmatrix}
\end{align}


I can raise the full stop using:

\begin{align}
\raisebox{\depth}{$\displaystyle\begin{pmatrix} a\\b \end{pmatrix} \displaystyle\begin{pmatrix} c\\d \end{pmatrix}$}\\
\end{align}


but this causes the problems mentioned above. Thanks for any help with this!

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That's why it's a bad idea to put the period at the bottom of the matrix: it should be at a position compatible with the =. So usually people consider matrices just like fractions: half above the baseline and half below it (almost). –  egreg Jan 21 '12 at 10:52
Hmm - I'll have to think about whether leaving . mid-line, level with =, will be OK. At the moment, the difference with their relative positions when matrices or fractions are inline, when = is higher than ., is looking a bit odd to me. –  Harry Macpherson Jan 21 '12 at 10:57
it's "standard" (or at least "house style") for most math publishers to consider the baseline with the = to be the one on which the period should be located. as for relative positioning of those two glyphs, the = is aligned vertically on the math axis, while the period sits on the actual baseline. a dot centered on the math axis would not be a period, but a \cdot. –  barbara beeton Jan 21 '12 at 13:12

You can put the dot in the sub-script, and then modify the font size and the spacing:

\documentclass{article}

\usepackage{amsmath}

% This prints a dot, slightly moved closer to the parenthesis and at the correct size.
\def\FullStop{{\kern-0.5ex\raise0.3ex\hbox{\normalsize.}}}

\begin{document}

\begin{align}
% You can place the full stop as a sub-script of the matrix.
\begin{pmatrix} a\\b \end{pmatrix} &= \begin{pmatrix} c\\d \end{pmatrix}_\FullStop\\
\intertext{Now}
\begin{pmatrix} e\\f \end{pmatrix} &= \begin{pmatrix} g\\h \end{pmatrix}
\end{align}

\end{document}
`
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