6

I have the equation in the twocolumn view

\documentclass[twocolumn]{article}
\usepackage{amsmath}
\begin{document}   

\begin{equation}
\begin{aligned}  
X(m) &= \frac{b-a}{N} \sum_{k=1}^{N} e^{-i2\pi (k-1)(m-1)/N} x(a + (b-a)\frac{k-1}{N}) \\ 
&= \frac{b-a}{N} \sum_{k=1}^{N} e^{-i2\pi (a + (b-a)\frac{k-1}{N})*\frac{m-1}{b-a}} \\
& x(a + (b-a)\frac{k-1}{N})e^{i2\pi a \frac{m-1}{b-a}} \\
& \xrightarrow{ N\to\infty } \int_{a}^{b} e^{-2\pi t \frac{m-1}{b-a}} x(t) dt\\
& e^{i2\pi a \frac{m-1}{b-a}} Qx(\frac{m-1}{b-a}). 
\end{aligned}
\end{equation}
\end{document}

Output

enter image description here

How would you present this equation in a twocolumn view?

  • Please don't just include snippets but a minimal code that can be typeset, from \documentclass{...} to \end{document}, removing the unnecessary code. – Alenanno Oct 18 '13 at 14:55
  • 1
    You mean aligned and not align, don't you? – karlkoeller Oct 18 '13 at 14:59
  • 1
    Are you saying that you don't like how it looks and you would want suggestions on how to have it look better? – karlkoeller Oct 18 '13 at 15:03
  • Don't nest align and equation environments. Both enter math-mode on their own, see this related question. – Qrrbrbirlbel Oct 18 '13 at 15:03
  • 2
    @Masi Use a_{k} instead of a+(b-a)\frac{k-1}{N}, to begin with. – egreg Oct 18 '13 at 15:36
11

You should be using split not align inside equation. Introducing new variables for large repeating expressions and shifting your indexing by one will reduce the size of the equation. Finally I introduce an eqbreak command to shift a split expression:

Sample output

\documentclass[twocolumn]{article}
\usepackage{amsmath, amsfonts, amssymb, textcomp}

\newcommand{\eqbreak}[1][2]{\\&\hskip#1em}

\begin{document}   

\begin{equation}
  \begin{split}  
    X(m+1)
    &= \frac{b-a}N \sum_{k=0}^{N-1} e^{-i2\pi km/N}\,  x(a_k) \\
    &= \frac{b-a}N \sum_{k=0}^{N-1} e^{-i2\pi a_km/(b-a)} \eqbreak[6]
    \times x(a_k)\,e^{i2\pi a m/(b-a)} \\
    &\xrightarrow{N\to\infty} e^{i2\pi a m/(b-a)} \,Qx\Bigl(\frac
    m{b-a}\Bigr),
  \end{split}
\end{equation}
where \( a_k = a + (b-a)k/N \).
\end{document}
  • As I just told to Marienplatz, I'm not sure that \times is the right symbol to use... – karlkoeller Oct 18 '13 at 15:47
  • 1
    @karlkoeller An alternative would be \cdot, but it depends on the wider context. – Andrew Swann Oct 18 '13 at 15:49
  • @Marienplatz There is no integral in the poster's example, nor is Qx explained. – Andrew Swann Oct 18 '13 at 15:52
  • I would go with \cdot... Anyway, as a mathematician, I would say that this is the only answer that looks good, IMHO. +1. – karlkoeller Oct 18 '13 at 15:59
  • 1
    @Masi I will comment on that question - you are missing alignment points. – Andrew Swann Aug 10 '16 at 12:47
3

I would propose you split the first two lines at a reasonably natural point. I would use explicit sizing instructions for the parentheses, and use \exp(...) expressions.

enter image description here

\documentclass[twocolumn]{article}
\usepackage{amsmath, amsfonts, amssymb, textcomp}
\begin{document}
\begin{align}
&X(m) \notag\\
&= \frac{b-a}{N} \sum_{k=1}^{N} \exp\bigl(-i2\pi (k-1)(m-1)/N\bigr) \notag\\
&\qquad  \times x\Bigl[a + (b-a)\frac{k-1}{N}\Bigr] \\
&= \frac{b-a}{N} \sum_{k=1}^{N} \exp\Bigl[-i2\pi \Bigl(a + (b-a)\frac{k-1}{N}\Bigr)
 \frac{m-1}{b-a}\Bigr] \notag \\
&\qquad  \times x\Bigl(a + (b-a)\frac{k-1}{N}\Bigr) 
        \exp\Bigl(i2\pi a \frac{m-1}{b-a}\Bigr) \\
& \xrightarrow{ N\to\infty } \exp\Bigl(i2\pi a \frac{m-1}{b-a}\Bigr) 
Qx\Bigl(\frac{m-1}{b-a}\Bigr)\,.
\end{align}
\end{document}
3

Just for fun!

\documentclass{article}
\usepackage[a4paper,margin=2cm,twocolumn]{geometry}
\usepackage{mathtools}
\begin{document}
\begin{equation}
\begin{split}  
X(m) 
&=
\!
\begin{multlined}[t]
    \frac{b-a}{N} \sum_{k=1}^{N} \Bigg[  x\left(a + \frac{k-1}{N}(b-a)\right)\\
    \times e^{-\frac{2\pi i (k-1)(m-1)}{N}} \Bigg]
\end{multlined}\\ 
&=
\!
\begin{multlined}[t]
    \frac{b-a}{N} \sum_{k=1}^{N}\Bigg[ x\left(a + \frac{k-1}{N}(b-a)\right) \\
    \times e^{2\pi i a \frac{m-1}{b-a}}\\
    \times e^{-2\pi i \left(a + \frac{k-1}{N}(b-a)\right)\times \frac{m-1}{b-a}}\Bigg]
\end{multlined}\\
& \xrightarrow{ N\to\infty }
\!
\begin{multlined}[t] 
    e^{2\pi i a \frac{m-1}{b-a}} \\
    \times \int_{a}^{b} e^{2\pi i a \frac{m-1}{b-a}} Qx\left(\frac{m-1}{b-a}\right).
\end{multlined}
\end{split}
\end{equation}
\end{document}

enter image description here

  • 1
    I'm not sure that \times is the right symbol to use... – karlkoeller Oct 18 '13 at 15:45

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.