7

I am trying to get

enter image description here

but I get

enter image description here

Here is my code:

\begin{align*}
F_1 = &\sum_{i=1}^{r^2+1} a_{i1}x_i^r \equiv 0 \pmod{p},\\
F_2 = &\sum_{i=1}^{r^2+1} a_{i2}x_i^r \equiv 0 \pmod{p},\\
      &\vdots \\
F_r = &\sum_{i=1}^{r^2+1} a_{ir}x_i^r \equiv 0 \pmod{p}.
\end{align*}
  • when you place the link for an image on a line with text, it will appear above the text, usually out of logical order. putting the link on a separate line, with a blank line between, keeps the intended order. i've applied that edit to your question so that it doesn't look like both the "desired" and "actual" outputs are produced by the same input. – barbara beeton Oct 3 '16 at 17:26
7

I'd place the vertical dots under the equals sign, to be honest.

Anyway, here's how you can do it and also how to align the summation signs by making the upper limits zero width:

\documentclass{article}

\usepackage{amsmath,mathtools}

\begin{document}

\begin{align*}
  F_1 &= \sum_{i=1}^{\mathclap{r^2+1}} a_{i1}x_i^r \equiv 0 \pmod{p},\\
  F_2 &= \sum_{i=1}^{\mathclap{r^2+1}} a_{i2}x_i^r \equiv 0 \pmod{p},\\
      & \phantom{\;=}\vdotswithin{\displaystyle\sum}\\
  F_r &= \sum_{i=1}^r a_{ir}x_i^r \equiv 0 \pmod{p}.
\end{align*}

\end{document}

enter image description here

  • This is the best answer. (Yes, I also provided an answer.) – JPi Oct 3 '16 at 16:31
5

You can set it in a similarly-sized box with the aid of eqparbox:

enter image description here

\documentclass{article}

\usepackage{amsmath,eqparbox}

\begin{document}

\begin{align*}
  F_1 = &\eqmakebox[sum]{$\displaystyle\sum_{i=1}^{r^2+1}$} a_{i1}x_i^r \equiv 0 \pmod{p},\\
  F_2 = &\eqmakebox[sum]{$\displaystyle\sum_{i=1}^{r^2+1}$} a_{i2}x_i^r \equiv 0 \pmod{p},\\
        &\eqmakebox[sum]{$\vdots$} \\
  F_r = &\eqmakebox[sum]{$\displaystyle\sum_{i=1}^r$} a_{ir}x_i^r \equiv 0 \pmod{p}.
\end{align*}

\end{document}

All content with the same <tag> in \eqmakebox[<tag>] are set in a box of similar width.

3

Since it is a visual arrangement anyway, I suggest to add the preferred space manually, like that.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align*}
F_1 = &\sum_{i=1}^{r^2+1} a_{i1}x_i^r \equiv 0 \pmod{p},\\
F_2 = &\sum_{i=1}^{r^2+1} a_{i2}x_i^r \equiv 0 \pmod{p},\\
      &\;\;\;\vdots \\
F_r = &\sum_{i=1}^r a_{ir}x_i^r \equiv 0 \pmod{p}.
\end{align*}
\end{document}

enter image description here

2
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{equation}
\begin{array}{rccl}
        F_1 &= &\sum\limits_{i=1}^{r^2+1} & a_{i1}x_i^r \equiv 0 \pmod{p},\\
        F_2 &= &\sum\limits_{i=1}^{r^2+1}& a_{i2}x_i^r \equiv 0 \pmod{p},\\
        &&\vdots &\\
        F_r &= &\sum\limits_{i=1}^r & a_{ir}x_i^r \equiv 0 \pmod{p}.
    \end{array}
\end{equation}
\end{document}

enter image description here

  • This has very awkward spacings around the equal signs. – gerw Oct 3 '16 at 18:34
  • Yes, it does.... – JPi Oct 3 '16 at 21:05
  • This is not really an equation, a lot of data aligned in an array. – pzorba75 Oct 4 '16 at 2:10

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