Im writing fraction in an equation. But then when I inserted $\frac{1}{2}$ inside the align*, error says missing }. I don't get it. Removing the code fraction will make my code work.


 Q(i,j) &= (n-2)d(i,j) - \sum_{k=1}^{n} d(i,k) - \sum_{k=1}^{n} d(j,k)    \\  \newline

  \delta (i,j) & =  $\frac{1}{2}$

  • you used an extra backslash right before \newline also, why did you pick \newline over `\`?
    – 1010011010
    Oct 5 '14 at 23:44
  • it has double backlash, i don't know why it don't appear. My real problem is why putting this $\frac{1}{2}$ brings error.
    – programmer
    Oct 5 '14 at 23:47

It should be

 Q(i,j) &= (n-2)d(i,j) - \sum_{k=1}^{n} d(i,k) - \sum_{k=1}^{n} d(j,k)    \\  
  \delta (i,j) & =  \frac{1}{2}

(of course, amsmath is called). Please observe that now there are no empty lines inside align* environment.

  • one other thing you didn't point out explicitly, but is essential: tje aalign environment is already math mode, so $ signs around the frac expression are not only not needed, they will result in an error message. Oct 6 '14 at 16:29

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