[Tex/LaTex] Aligning equations with align*

align

I wanted to align a set of equations to left. I found on the Internet that you can do it easily with align* environment.

I found it here: http://en.wikibooks.org/wiki/LaTeX/Advanced_Mathematics

So I did it:

\begin{align*}

f(b)-f(a)=&f((b_1,b_2,\dots,b_k))-f((a_1,a_2,\dots,a_k))=\
&=\sum_{i=1}^{k}[f((a_1,\dots,a_{i-1},b_i,\dots, b_k))-f((a_1,\dots,a_i,b_{i+1},\dots, b_k)) 
\end{align*}

Unfortunately, I got bunch of red errors saying that there are missing $s. Why? Doesn't that align* environment provide a math environment already?

Best Answer

You can't have blank lines within an align environment:

enter image description here

Notes:

AS Werner (and egreg) commented, you should use &= as opposed to =&.
And to answer your other question, you and correct in that you do not use $ within an align as that is already math mode.
I removed the 2nd equal sign in the first line as it is not necessary.
I added \Big[ and \Big] to provide larger square brackets -- your right bracket was missing.

Code:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{align*}
f(b)-f(a) &=f((b_1,b_2,\dots,b_k))-f((a_1,a_2,\dots,a_k))\\
          &=\sum_{i=1}^{k}\Big[f((a_1,\dots,a_{i-1},b_i,\dots, b_k))-f((a_1,\dots,a_i,b_{i+1},\dots, b_k)) \Big]
\end{align*}

\end{document}

Related Solutions

[Tex/LaTex] Alignement in columns and spacing between columns of an equations environment

There are quite a few ways you could achieve your desired output- using the amsmath environments that you mentioned is certainly an option. Of course, you should make sure to avoid eqnarray as discussed in eqnarray vs align

Another option is to use the array environment

enter image description here

\documentclass{article}

\begin{document}

\[
\begin{array}{cccll}
    x< & a  & =     & 1     & i<j\\
    x< & b  & =     & 12        & <i<j\\
    x< & c  & =     & 123       & <i<j<k
\end{array}
\]
\end{document}

This has the advantage that you can easily control column spacing, for example

\begin{array}{c@{\hspace{1cm}}ccll}
        x< & a  & =     & 1     & i<j\\
        x< & b  & =     & 12        & <i<j\\
        x< & c  & =     & 123       & <i<j<k
\end{array}

gives

enter image description here

[Tex/LaTex] Aligning sub-equations within align

Use the \bigg variety for bigger delimiters and align the sums. There's a subtlety for the last one, since the long subscript would shift it to the right and \mathclap from mathtools avoids it.

\documentclass{article}

\usepackage{amsmath,amssymb,mathtools}
\DeclareMathOperator*{\argmax}{argmax}
\begin{document}
\begin{equation}\label{eq:BILP}
\begin{split}
I^* = \argmax_{\mathcal{I}}\biggl\{
  & \sum_{i\in \mathcal{V}} (\theta_K \cdot \mathbb{I}_{i,j}(1,1) + \theta_K \cdot \mathbb{I}_{i,j}(0,0) ) + {}\\
  & \sum_{i\in \mathcal{E}} \theta_{i_0} \cdot \mathbb{I}(x_i=0) + \theta_{i_1} \cdot \mathbb{I}(x_i=1) \biggr\}\\
\text{s.t.}\quad
  & \sum_{x_j} \mathbb{I}_{i,j}(1,x_j)  = \mathbb{I}(x_i=1) \\
  & \sum_{x_i}\mathbb{I}_{i,j}(x_i,1) = \mathbb{I}(x_j=1) \\
  & \sum_{\mathclap{x_i,x_j}}\mathbb{I}_{i,j}(x_i,x_j) = 1 
\end{split}
\end{equation}
\end{document}

enter image description here

Best Answer

Notes:

Code:

Related Solutions

[Tex/LaTex] Alignement in columns and spacing between columns of an equations environment

[Tex/LaTex] Aligning sub-equations within align

Related Question