How do I display a slightly long equation in one line?

I want to write the following in one line

\documentclass{article}
\usepackage{amsmath}
\begin{document}

$\left |\hspace{0.1cm}\int \limits_{\Omega_1 \times \Omega_2 \times \cdots \times \Omega_{n-1}}\left|\int_{\Omega_n}\overline{f_{x_1, \cdots ,x_{n-1}}}e_{nj_n}\,d{\mu_n}\right|^2\,d{(\mu_1 \times \cdots \times \mu_{n-1})}\right|\leq\left|\hspace{0.1cm}\int \limits_{\Omega_1 \times \Omega_2 \times \cdots \times \Omega_{n-1}} \int_{\Omega_n}\left( \overline{f_{x_1, \cdots ,x_{n-1}}}\right)^2. 1\,d{\mu_n}\,d{(\mu_1 \times \cdots \times \mu_{n-1})}\right|$

\end{document}


Is there any way?

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I'd use a notation to the product. For example, bold face for the products. –  Sigur Jul 22 at 2:42
Thank you so much for editing and replying, I am new here. Coming to the problem, I am writing some notes, to get a feel of what I want to convey, I would like to have the product there, is there any other way? Like decreasing the font size for this particular line or something like that? I don't know to do this –  Tiju Cherian John Jul 22 at 2:47
Why no split the equation by \leq? So it would fit in any document. –  skpblack Jul 22 at 2:53
Otherwise would reduce margins (or font size) or put it in landscape mode. Nothing is very fancy. –  skpblack Jul 22 at 2:56

I'm not in a position to comment on your math, hence the following comments are strictly about improving the appearance of the typeset result.

• Your equation isn't just "slightly long", unless you have a truly enormous text block. As the answer by @Sigur has also already suggested, you need to use a math environment that allows a line break. Since it doesn't look like you need to number the equation, the multline* environment, which is provided by the amsmath package, may be suitable.

• Instead of typing \left| and \right| to generate the absolute value bars, it's better to use a more "LaTeX-y" approach and create a macro. One such method is to define a macro called \abs using the machinery of the mathtools package (pun intended).

• Regarding the use of typographic ellipses ("dot dot dot"): Dots between commas are usually set on the baseline, whereas those between binary operators (such as \times) are generally set on the mathline. However, rather than \dotsc and \dotsm explicitly, its better to just write \dots and let LaTeX figure out how to typeset the ellipses.

• There's little point in writing d{\mu_n}. The curly braces around \mu_n don't "do" anything except convert their contents into an atom of type "math ordinary"; however, \mu_n happens to be of type "math ord" anyway, so the curly braces just add clutter. Better to write d\mu_n.

• You could use a few more \, (thinspace) and \! (negative thinspace) directives to arrange the material in a slightly more pleasing way.

\documentclass{article}
\usepackage{mathtools}
\DeclarePairedDelimiter{\abs}{\lvert}{\rvert}

\begin{document}
\begin{multline*}
\abs*{\,\int \limits_{\Omega_1 \times \Omega_2 \times \dots \times \Omega_{n-1}}
\abs*{\int_{\Omega_n}\!
\overline{f_{x_1, \dots ,x_{n-1}}}\,e_{nj_n}\,d\mu_n}^2
d{(\mu_1 \times \dots \times \mu_{n-1})}}\\
\leq\abs*{\,\int \limits_{\Omega_1 \times \Omega_2 \times \dots \times \Omega_{n-1}} \!
\int_{\Omega_n}\left(\,\overline{f_{x_1, \dots ,x_{n-1}}}\,\right)^2\,d\mu_n
d(\mu_1 \times \dots \times \mu_{n-1})}
\end{multline*}
\end{document}

-
Thank You so much for a very helpful answer. But I did not understand what do you mean by "LaTeX-y" approach and what is the difference \abs way does? I am sorry that I am just learning the basics of tex –  Tiju Cherian John Jul 22 at 5:25
@TijuCherianJohn - By adopting a "LaTeX-y" approach, I meant keeping the two things as much as possible separate: the items that are actually typeset (in this case, the tall vertical bars) and the command that you enter to inform LaTeX that tall vertical bars should be placed to the left and right of some group of math elements. By setting up macros named \abs and \abs* (the latter resizes the vertical bars automatically), you are left free to code your math in a way that emphasizes the meaning of the code rather than just its immediate looks. –  Mico Jul 22 at 5:34

Suggestion:

\documentclass{report}
\usepackage{amsmath}

\begin{document}

\begin{multline*}
\left|\, \int_{%
\Omega_1 \times \cdots \times \Omega_{n-1}}%
\left|\, \int_{%
\Omega_n} \overline{f}_{x_1, \ldots ,x_{n-1}}\,%
e_{nj_n}\, d{\mu_n}%
\right|^2\, d{(\mu_1 \times \cdots \times \mu_{n-1})}\,%
\right| \leq \\
%
\left|\, \int_{%
\Omega_1 \times \cdots \times \Omega_{n-1}}%
\int_{\Omega_n}%
\overline{f}^2_{x_1, \ldots ,x_{n-1}} \cdot %
1\, d{\mu_n}\, d(\mu_1 \times \cdots \times \mu_{n-1})\,
\right|
\end{multline*}

\end{document}


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Should the inner pair of vertical bars in the upper line maybe be slightly smaller than the outer pair? –  Mico Jul 22 at 8:07
@Mico, it could be. I don't know what is better. I liked your answer. –  Sigur Jul 22 at 12:25