Math & Science ⇒ split numerator over two lines

[huki1]

Hello,
I have a long fraction that doesn't fit on a page:

Code: Select all

\vec{u}_{i+1/2,j,k} = \left(u_{i+1/2,j,k}, \frac{v_{i,j-1/2,k}+v_{i,j+1/2,k}+v_{i+1,j-1/2,k}+v_{i+1,j+1/2,k}}{4}, \frac{w_{i,j,k-1/2}+w_{i,j,k+1/2}+w_{i+1,j,k-1/2}+w_{i+1,j,k+1/2}}{4} \right)

,

What I would like to do, is to split the numerator over two lines and get sth like that:

I tried to look for a solution but without any results so far.

Thanks in advance.

[Stefan Kottwitz]

Hi,

you could use an array environment for the numerator.

Stefan

[huki1]

you could use an array environment for the numerator.

Yes, but i thought there is a more elegant solution. Besides, the equation is a part of

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\begin{subequations}
\begin{align}
.... %subequations here
\vec{u}_{i,j,k+1/2} &= \left(\frac{u_{i-1/2,j,k}+u_{i+1/2,j,k}+u_{i-1/2,j,k+1}+u_{i+1/2,j,k+1}}{4}, \frac{v_{i,j-1/2,k}+v_{i,j+1/2,k}+v_{i,j-1/2,k+1}+v_{i,j+1/2,k+1}}{4}, w_{i,j,k+1/2} \right). \\
.... %subequations here
\end{align}
\end{subequations}

[huki1]

There actually is a good solution for the problem I encountered. The key is \atop. For example:

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\frac{{a+b+ \atop c+d}}{4}