Resize equation/Aligning equation/

Question

I am writing my thesis but some of the equation widths is more than the text width.for example

\begin{eqnarray}\label{eq7}
\Theta(m+2)&=&\frac{1}{(m+1)(m+2)}\Bigg[N^2\,\Theta(m)-N^2\,\theta_{a}\delta(m)+
N_{r}\,\sum_{\ell=0}^{m}\sum_{k=0}^{\ell}\sum_{j=0}^{k}\phi(j)\phi(k-j)\phi(\ell-k)\phi(m-\ell)\nonumber\\&&
-PeS\sum_{\ell=0}^{m}\delta(\ell-1)(m-\ell+1)\Theta(m-\ell+1)-Pe\,(m+1)\,\Theta(m+1)-N_{r}\,\theta_{s}\,\delta(m)\Bigg].
\end{eqnarray} 

What can I do to fit text width?

I try to write the equation fit to text width

Answer 1

I am not sure you can actually fit the equation to the text width as it is very long. You may try by using a smaller font size but I doubt this will work.

I would actually suggest another approach by splitting the terms in different equations and bringing the whole thing as a much smaller equation. This obviously may not be possible depending on how you are able to write things.

\documentclass[11pt, a4paper, twoside]{article}
\usepackage{mathtools}                      
\usepackage[a4paper]{geometry}
\begin{document}
\begin{align}\label{eq7}
X_1 =& N^2\,\Theta(m)-N^2\,\theta_{a}\delta(m)+ N_{r}\sum_{\ell=0}^{m}\sum_{k=0}^{\ell}\sum_{j=0}^{k}\phi(j)\phi(k-j)\phi(\ell-k)\phi(m-\ell) \\
X_2 =& -PeS\sum_{\ell=0}^{m}\delta(\ell-1)(m-\ell+1)\Theta(m-\ell+1) \\
X_3 =& -Pe\,(m+1)\,\Theta(m+1)-N_{r}\,\theta_{s}\,\delta(m) \\
\Theta(m+2) =& \frac{1}{(m+1)(m+2)}\Bigg[X_1 + X_2 + X_3\Bigg]
\end{align} 
\end{document}

I know this is not what you asked but I hope this may still help.

You may also want to try the split environment that comes within the amsmath or mathtools packages. It will allow you to manually break the equation in several lines but numbering the whole equation as only one.

Lastly, this document provides an interesting discussion about the eqnarray environment being more destructive than useful for the document. The align environment should be prefered (when possible).

Clézard