Font size inside subequations environment!

How I can change the font size inside the subequations environment? See below:

$$\textstyle \xi_{1} = A + B + C;$$


The command \textstyle works fine inside the equation environment, but inside the subequations environment (see below, again) does not works.

\begin{subequations}
\textstyle
\begin{eqnarray}
\xi_{1} = A + B + C \\
\xi_{2} = E + F + G \\
\xi_{3} = H + I + J
\end{eqnarray}
\end{subequations}


I give errors:

"Missing \$ inserted.", "Missing \endgroup inserted.", "You can't use \halign in math mode", etc.

If I put \textstyle inside eqnarray it works, but then I need put in all equations.

Please, how I can change the math font size inside the subequations environment?

• Welcome to TeX.SE. You need to move the \textstyle to be after \begin{eqnarray}. But, why do you want to do that? Also, you should avoid eqnarray as per this question. Nov 4 '14 at 17:39
• If I put \textstyle after \begin{eqnarray} it is applied only to first equation. :(( Nov 4 '14 at 17:43
• The eqnarray environment is badly deprecated and shouldn't be used anymore, in any LaTeX document. For more information see the posting eqnarray vs align.
– Mico
Nov 4 '14 at 18:53

Define an alignts environment that's the same as align, but uses \textstyle throughout.

The problem with long alignments is solved by issuing \allowdisplaybreaks. I tested with 216 equations without any problem. Don't use eqnarray under any circumstances.

\documentclass{article}
\usepackage{amsmath}
\usepackage{etoolbox}

\makeatletter
\let\alignts@preamble\align@preamble
\patchcmd{\alignts@preamble}{\displaystyle}{\textstyle}{}{}
\patchcmd{\alignts@preamble}{\displaystyle}{\textstyle}{}{}

\def\alignts{\let\align@preamble\alignts@preamble\start@align\@ne\st@rredfalse\m@ne}
\let\endalignts\endalign
\makeatother

\allowdisplaybreaks

\begin{document}
\begin{alignts}
\xi_{1} &= \sum_{i=1}^n a_i \\
\xi_{2} &= \int_a^b f(x)\,dx \\
\xi_{3} &= \bigvee_i v_i
\end{alignts}
\end{document}


Embed this in a subequations environment, the result will be the same as subequations only changes the equation counter and has no influence on the typesetting of the equations.

If you insist in using eqnarray, it's just the same:

\documentclass{article}
\usepackage{amsmath}
\usepackage{etoolbox}

\makeatletter
\let\eqnarrayts\eqnarray
\patchcmd{\eqnarrayts}{\displaystyle}{\textstyle}{}{}
\patchcmd{\eqnarrayts}{\displaystyle}{\textstyle}{}{}
\let\endeqnarrayts\endeqnarray
\makeatother

\allowdisplaybreaks

\begin{document}

\begin{eqnarrayts}
\xi_{1} = \sum_{i=1}^n a_i \\
\xi_{2} = \int_a^b f(x)\,dx \\
\xi_{3} = \bigvee_i v_i
\end{eqnarrayts}

\end{document}

• Hi @egreg, thanks by your attention. This seems a good approach and it works to more equations as I need. But when I try use it in my big text using memoir class nothing happens. Why?! :( Nov 5 '14 at 1:26
• @user901366 I see no difference if I change article into memoir, so I guess there's more that this. Try making a minimal example and to be more specific about “nothing happens”, but in a new question. Nov 5 '14 at 10:45
• Ok, in your MWE works, then is a useful answer, thanks! I will investigate better the problem with memoir. Nov 5 '14 at 12:48