General ⇒ An issue with a multiline formula

[Rc3g]

Hi, I'm trying to typeset a definition, but I'm not getting things aligned the way I want them to. This is the code:

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\begin{eqnarray*}
p_n & = m_{(n)} = \sum_{i} x_i^n,			& n \geq 1 \\
p_{\lambda} & = p_{\lambda_1} p_{\lambda_2} \dotsb,	& \text{if } \lambda = (\lambda_1, \lambda_2, \dotsc).
\end{eqnarray*}

and as you can see in the attached image, the first equals sign in each row are not aligning properly. Can anything be done about this?

[balf]

First, you shouldn't use eqnarray: it is obsolete and it may give bad spacing. Load amsmath instead, and the align* environment:

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\begin{align*}
p_n & = m_{(n)} = \sum_{i} x_i^n,         \quad n \geq 1 \\
p_{\lambda} & = p_{\lambda_1} p_{\lambda_2} \dotsb,   \quad \text{if } \lambda = (\lambda_1, \lambda_2, \dotsc).
\end{align*}

I'm not sure whether the second alignment is necessary: if you want it, just write

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\begin{align*}
p_n & = m_{(n)} = \sum_{i} x_i^n,         && n \geq 1 \\
p_{\lambda} & = p_{\lambda_1} p_{\lambda_2} \dotsb,   &&\text{if } \lambda = (\lambda_1, \lambda_2, \dotsc).
\end{align*}

and if you want to specify the horizontal space between the two columns, say 1em, use:

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\begin{alignat*}{2}
p_n & = m_{(n)} = \sum_{i} x_i^n,         &\quad &n \geq 1 \\
p_{\lambda} & = p_{\lambda_1} p_{\lambda_2} \dotsb,   && \text{if } \lambda = (\lambda_1, \lambda_2, \dotsc).
\end{alignat*}

B.A.

[localghost]

As balf already stated there are some very good reasons not to use the eqnarray environment [1]. The amsmath package provides some useful environments. Refer to its manual.

[1] The PracTeX Journal, TeX Users Group | Lars Madsen: Avoid eqnarray!


Best regards
Thorsten¹

[Rc3g]

Thanks, your last example was exactly what I was looking for.

First, you shouldn't use eqnarray: it is obsolete and it may give bad spacing. Load amsmath instead, and the align* environment:

Well, to be honest I did use align* at first for this formula, but I thought it looked worse than eqnarray!