# Same size for equation over multiple lines with norm

I want to have an equation written over multiple lines but without the sizes varying too much. An example would be

\begin{align*}
||f||&=||(t\mapsto\int_0^t g(s)ds)||+||A||\\
&\leq a+b
\end{align*}


The problem then is:
-The norm signs are too small. This can be changed by using \left, \right and \middle but then the left hand side is of a different size
-Or integral sign is very small if I use textstyle to compress it's size

A solution which could look nice would be something like

\begin{align*}
||f||&=\left|\middle|\middle(t\mapsto\textstyle{\int_0^t} g(s)ds\middle)\middle|\middle|+\middle|\middle|A|\right|\\
&\leq a+b
\end{align*}


However it still looks strange as the left hand side is still small and I don't know how this could be changed. Are there any recommendations how to write such equations aesthetically?

• Apart from the fact that typing norms with || is wrong (see e.g.tex.stackexchange.com/a/43009/82917) why would you want the norm to have the same size on both sides of the equation? Aug 2 at 16:24
• Thanks for the tip. I think it looks unpleasant otherwise. Aug 2 at 16:26

Defining \norm properly (e.g. with mathtools) is the first step.

\documentclass[twocolumn]{article}

\usepackage{mathtools}
\DeclarePairedDelimiter{\norm}{\|}{\|}

\begin{document}

You seem to want this:
\begin{align*}
\norm[\Big]{f}&= \norm[\Big]{\Bigl(t\mapsto\textstyle\int_0^t g(s) \, ds\Bigr)} + \norm[\Big]{A}\\
&\leq a+b .
\end{align*}
IMNSHO this is \emph{far} better:
\begin{align*}
\norm{f}&= \norm[\Big]{\Bigl(t\mapsto\textstyle\int_0^t g(s) \, ds\Bigr)} + \norm{A}\\
&\leq a+b .
\end{align*}

\end{document}


If you think the first version looks more pleasant, then we have quite a different taste :-)

• I've added a small space \, before the differential.
• \textstyle does not take an argument. By writing \textstyle{\int_0^t} you just switch to \textstyle for the rest of the current group, and putting \int_0^t in braces changes the integral from an operator to a ordinary symbol, which results in wrong spacing. I just removed the braces, as \textstyle does no harm in what follows. Alternatively you could use \mathop{\textstyle\int_0^t}.