Same size for equation over multiple lines with norm

Question

I want to have an equation written over multiple lines but without the sizes varying too much. An example would be
begin{align*}
||f||&=||(tmapstoint_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(tmapstotextstyle{int_0^t} g(s)dsmiddle)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?

campa · Answer

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(tmapstotextstyleint_0^t g(s) , dsBigr)} + norm[Big]{A}
     &leq a+b .
end{align*}
IMNSHO this is emph{far} better:
begin{align*}
norm{f}&= norm[Big]{Bigl(tmapstotextstyleint_0^t g(s) , dsBigr)} + 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 :-)
Small comments:

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{textstyleint_0^t}.

Same size for equation over multiple lines with norm

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