Centering split equation

Question

I am quite new to TeX. I want that each line in the following equation be centered, but I cannot find how to do it.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{equation}
\begin{split}
a & = \frac{M_{20}}{M_{00}} - x^{2}_{c}, \;\;\;
b = 2(\frac{M_{11}}{M_{00}} - x_{c}y_{c}), \;\;\;
c = \frac{M_{02}}{M_{00}} - y^{2}_{c}, \\
&\quad x_{c} = \frac{M_{10}}{M_{00}}, \;\;\;
y_{c} = \frac{M_{01}}{M_{00}}, \\
&\quad M_{ij} = \displaystyle\sum\limits_{x} \displaystyle\sum\limits_{y} x^i y^j I(x,y)
\end{split}
\end{equation}
\end{document}

Also, it would be awesome if I could write "and" after the first line ;)

Thanks in advance

Check out Philipp's answer. Embedding of gathered in equation puts one centered equation number nexts to centered equations. The accepted answer forces the equation number onto the last line and a large number of \notag commands. — Argyll, May 02 '14 at 11:51

score 38 · Answer 1 · edited Jul 15 '17 at 13:58

38

Just replace the split environment by gathered, then you don't have to suppress spurious equation numbers:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{equation}
\begin{gathered}
a = \frac{M_{20}}{M_{00}} - x^{2}_{c}, \;\;\;
b = 2(\frac{M_{11}}{M_{00}} - x_{c}y_{c}), \;\;\;
c = \frac{M_{02}}{M_{00}} - y^{2}_{c}, \\
\quad x_{c} = \frac{M_{10}}{M_{00}}, \;\;\;
y_{c} = \frac{M_{01}}{M_{00}}, \\
\quad M_{ij} = \displaystyle\sum\limits_{x} \displaystyle\sum\limits_{y} x^i y^j I(x,y)
\end{gathered}
\end{equation}
\end{document}

edited Jul 15 '17 at 13:58

David Carlisle

757,742

answered Jan 19 '11 at 14:35

Philipp

17,641

3

This should be definitely the right answer... – GiuTeX Aug 05 '17 at 10:17
1

@GiuTeX why? Is it significantly different from the accepted answer? – Nathan majicvr.com Dec 05 '21 at 22:34
1

@Nathan gotta be honest with you I don't remember at all why I wrote that. Looking now at the accepted answer I can't say there are substantial differences... – GiuTeX Dec 07 '21 at 10:53
1

@GiuTeX other voters seem to agree with you, though. I suppose the abstracting-away of other subtleties and just leaving the votes to speak probably mean you're right – Nathan majicvr.com Dec 07 '21 at 21:52

score 18 · Accepted Answer · edited Jun 08 '17 at 13:28

18

\documentclass{minimal}
\usepackage{amsmath}

\begin{document}

\begin{gather}
a  = \frac{M_{20}}{M_{00}} - x^{2}_{c},\quad
b = 2(\frac{M_{11}}{M_{00}} - x_{c}y_{c}),\quad
c = \frac{M_{02}}{M_{00}} - y^{2}_{c},\nonumber\\[1ex]
\text{and}\nonumber\\[1ex]
x_{c} = \frac{M_{10}}{M_{00}},\quad
y_{c} = \frac{M_{01}}{M_{00}}, \nonumber\\
M_{ij} = \displaystyle\sum\limits_{x} \displaystyle\sum\limits_{y} x^i y^j I(x,y)
\end{gather}

\end{document}

alt text

edited Jun 08 '17 at 13:28

samcarter_is_at_topanswers.xyz

158,329

answered Jan 19 '11 at 10:36

Jake

232,450

Instead of \displaystyle\sum\limits_{x} you can write \sum_{x} – Bruno Le Floch Jan 19 '11 at 11:07
1

or \sum_x... :-) – Jan 19 '11 at 11:17
I used '\displaystyle\sum\limits_{x}' since the position of limit is a little bit different from '\sum_{x}'. With '\displaystyle\sum\limits_{x}' it actually goes below '\sum'. – nacho4d Jan 19 '11 at 12:11
Inside an equation environment it is already at displaystyle, and the subscript will be placed below. amsmath also defined the \intertext{} command which is made for exactly for inserting a short text between equations like this. – Mikael Öhman Jan 19 '11 at 12:41

score 4 · Answer 3 · edited Jun 09 '17 at 15:46

The code below is not exactly what you asked for, but it has some alternatives that you might want consider.

Use \left and \right to fix the size of the parenthesis
Use \intertext to put words between equations
Use & to get better control of alignment

You mentioned you are new. You might want to read the mathtools document.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align}
a &= \frac {M_{20} } {M_{00} } - x^{2}_{c} , &
b &= 2 \left (  \frac {M_{11} } {M_{00} } - x_{c} y_{c}  \right )  , & %NOTE THE \LEFT AND \RIGHT
c &= \frac {M_{02} } {M_{00} } - y^{2}_{c} , \\
\intertext {and} % NOTE THE 'CORRECT' USAGE OF INTERTEXT TO WRITE IN BETWEEN EQUATIONS
&& \quad x_{c} &= \frac {M_{10} } {M_{00} } , & % NOTE THE DOUBLE && TO ALIGN TO THE SECOND COLUMN
y_{c} &= \frac {M_{01} } {M_{00} } , \\
\intertext {Some text}
&& \quad M_{ij} &= \sum \limits_{x} \sum \limits_{y} x^i y^j I( x, y )
\end{align}
\end{document}

score 3 · Answer 4 · edited Jun 09 '17 at 15:46

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

\begin{gather}
a = \frac{M_{20}}{M_{00}} - x^{2}_{c}, \;\;\; 
    b = 2\left(\frac{M_{11}}{M_{00}} - x_{c}y_{c}\right), \;\;\;
    c = \frac{M_{02}}{M_{00}} - y^{2}_{c}, \nonumber\\
x_{c} = \frac{M_{10}}{M_{00}}, \;\;\; y_{c} = \frac{M_{01}}{M_{00}}, \\
M_{ij} = \sum_x\sum_y x^i y^j I(x,y)\nonumber
\end{gather}

\end{document}

Centering split equation

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