# Increase size of fractions on multiple lines

Inside a matrix, I have some very loaded (subscripts, greek letters, \breve) fractions:

$$Q_r = \begin{bmatrix} \frac{\partial \breve{y}_r}{\partial \theta_1}\bigg|_{t_1} & \cdots & \frac{\partial \breve{y}_r}{\partial \theta_p}\bigg|_{t_1} \\ \vdots & \ddots & \vdots \\ \frac{\partial \breve{y}_r}{\partial \theta_1}\bigg|_{t_{N_{sp}}} &\cdots & \frac{\partial \breve{y}_r}{\partial \theta_p}\bigg|_{t_{N_{sp}}}\\ \end{bmatrix}$$


The fractions look to me too small compared to \bigg|. I tried \medskip but it was not effective.

How can I increase their size and/or spacing to make them a better fit?

p.s. I know they are not aligned, but readability comes before neatness.

• Have you tried \dfrac and \bigr|? – LaRiFaRi Jun 22 '15 at 14:25
• @LaRiFaRi isn't dfrac for stacked fractions? – laureapresa Jun 22 '15 at 14:29
• @writingthesis - "dfrac" is short for "display-style fraction". (The elements in a bmatrix enviroments are typeset in text-style math mode, not display-style math mode.) – Mico Jun 22 '15 at 14:41

I can think of two solutions:

• Use \dfrac ("display-style fraction") instead of \frac to increase the size of the fractional terms, and

• Keep using \frac, but reduce the size of the conditioning bars from \bigg to \Big.

Both methods are acceptable, typographically speaking. Which one is "better" will depend on many aspects of your documents (about which we know nothing).

\documentclass{article}
\usepackage{amsmath} % for "bmatrix" environment and "\dfrac" macro
\begin{document}

Method 1: Use \verb+\dfrac+ instead of \verb+\frac+
$Q_r = \begin{bmatrix} \dfrac{\partial \breve{y}_r}{\partial \theta_1}\bigg|_{t_1} & \cdots & \dfrac{\partial \breve{y}_r}{\partial \theta_p}\bigg|_{t_1} \\ \vdots & \ddots & \vdots \\ \dfrac{\partial \breve{y}_r}{\partial \theta_1}\bigg|_{t_{N_{\textit{sp}}}} &\cdots & \dfrac{\partial \breve{y}_r}{\partial \theta_p}\bigg|_{t_{N_{\textit{sp}}}}\\ \end{bmatrix}$

\bigskip
Method 2: Reduce the size of the vertical bars to \verb+\Big+
$Q_r = \begin{bmatrix} \frac{\partial \breve{y}_r}{\partial \theta_1}\Big|_{t_1} & \cdots & \frac{\partial \breve{y}_r}{\partial \theta_p}\Big|_{t_1} \\ \vdots & \ddots & \vdots \\ \frac{\partial \breve{y}_r}{\partial \theta_1}\Big|_{t_{N_{\textit{sp}}}} &\cdots & \frac{\partial \breve{y}_r}{\partial \theta_p}\Big|_{t_{N_{\textit{sp}}}}\\ \end{bmatrix}$

\end{document}


In addition to Mico and in order to show the \right| command:

% arara: pdflatex

\documentclass{article}
\usepackage{mathtools}
\newcommand*{\partderat}[3]{\left.\dfrac{\partial#1}{\partial#2}\right|_{\mathrlap{#3}\phantom{t_{N_{\textit{sp}}}}}}
\begin{document}
$Q_r = \begin{bmatrix} \partderat{\breve{y}_r}{\theta_1}{t_1} & \cdots & \partderat{\breve{y}_r}{\theta_p}{t_1} \\ \vdots & \ddots & \vdots \\[\jot] \partderat{\breve{y}_r}{\theta_1}{t_{N_{\textit{sp}}}}&\cdots & \partderat{\breve{y}_r}{\theta_p}{t_{N_{\textit{sp}}}}\\ \end{bmatrix}$
\end{document}


Note that it is very wise to use custom commands for this. Like this, you can switch between \dfrac and \frac later on. Or you can replace the automatic \right| by something fix when you have found your desired height.