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I'm trying to vertically align two equations but I fail to get it right.

$\begin{aligned} 
   f_{s_{i}}=-\frac{w_{s}}{n_{i}}\sum_{j=1}^{n}g(d_{ij})d_{ij} \\
    g(d_{ij}) =
  \begin{cases} 
    1 & d_{ij}\leq r_{h}\\
    exp(-\frac{(d_{ij}-r_{h})^{2}}{\sigma^{2}})   & d_{ij}> r_{h}
  \end{cases}
\end{aligned}$  

I get the following: enter image description here

How can I align the equation 'f' and 'g' knowing that they are presented in a table?

2 Answers 2

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You can use on these, depending on whether you want to align the = signs or the beginning of each line. Remember that aligned (or align) requires marking the alignment point with an ampersand:

$\begin{aligned} 
   f_{s_{i}} &=-\frac{w_{s}}{n_{i}}\sum_{j=1}^{n}g(d_{ij})d_{ij} \\
    g(d_{ij}) &=
  \begin{cases} 
    1 & d_{ij}\leq r_{h}\\
    \exp\Bigl(-\frac{(d_{ij}-r_{h})^{2}}{\sigma^{2}}\Bigr)   & d_{ij}> r_{h}
  \end{cases}
\end{aligned}$ 

$\begin{aligned} 
   &f_{s_{i}} =-\frac{w_{s}}{n_{i}}\sum_{j=1}^{n}g(d_{ij})d_{ij} \\
   &g(d_{ij})  =
  \begin{cases} 
    1 & d_{ij}\leq r_{h}\\
    \exp\bigl(-\frac{(d_{ij}-r_{h})^{2}}{\sigma^{2}}\bigr)   & d_{ij}> r_{h}
  \end{cases}
\end{aligned}$   

I added two different sizes for the parentheses after exp in the two proposed codes.

Unrelated: like all usual functions having a name, the exp function should typed in upshape, which is obtained with the command \exp (like \sin, \cos, \log, &c.)

enter image description here

6
  • 1
    +1. I would increase the size of the round parentheses around the fraction term in the second row of the cases environment, though.
    – Mico
    Jan 28, 2020 at 13:00
  • @Mico: You're right. I didn't have time when I , posted to check this point, but I've added size commands (different in each proposed code, as none is perfect in this respect). Thanks for reminding me!
    – Bernard
    Jan 28, 2020 at 18:42
  • It's more usual to set such expressions in display form, not as in-line math. Jan 28, 2020 at 20:02
  • @barbarabeeton: I don't think that, for the fraction in the cases environment, the display form looks so nice. Personally, I would rather use \mfrac, but I didn't want to complexify my answer.
    – Bernard
    Jan 28, 2020 at 20:15
  • Okay, legitimate personal preference. But then you're giving up the horizontal centering, "separation" above and below, and possibility of numbering, that come with a display environment. (I really hate to encourage the use of \\ to break lines, and just setting something like this as a separate paragraph would probably result in followup questions.) Jan 28, 2020 at 21:37
2

You just need to use the & charactere whereever you want to put the alignment.

For example, if you want to align at the left side of the column:

$\begin{aligned} 
   & f_{s_{i}}=-\frac{w_{s}}{n_{i}}\sum_{j=1}^{n}g(d_{ij})d_{ij} \\
   & g(d_{ij}) =
  \begin{cases} 
    1 & d_{ij}\leq r_{h}\\
    exp(-\frac{(d_{ij}-r_{h})^{2}}{\sigma^{2}})   & d_{ij}> r_{h}
  \end{cases}
\end{aligned}$ 

else, if you want to align in the = charactere, you do as:

$\begin{aligned} 
   f_{s_{i}} & =-\frac{w_{s}}{n_{i}}\sum_{j=1}^{n}g(d_{ij})d_{ij} \\
   g(d_{ij}) & =
  \begin{cases} 
    1 & d_{ij}\leq r_{h}\\
    exp(-\frac{(d_{ij}-r_{h})^{2}}{\sigma^{2}})   & d_{ij}> r_{h}
  \end{cases}
\end{aligned}$ 
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  • Welcome to TEX.SE! What difference is there between Bernard's answer and yours?
    – campa
    Jan 28, 2020 at 14:00
  • I actually didn't read his code (just now that you said), I just did with examples and explained the cases. Whereas he hasn't. Anyway, the two will give the same result. Jan 28, 2020 at 14:03

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