7

I have the following equation in my tex document:

\documentclass{article}
\begin{document}
  \begin{equation}
    x_{ij} = \frac{
                \sum_{t}{e_i(t)e_j(t)}
             } { 
                \sqrt{\sum_t{e_i^2(t)}} 
                \sqrt{\sum_t{e_j^2(t)}}
             }
  \end{equation}
\end{document}

The equation is printed like this:

demo equation

The problem is that despite having almost the same content, the two square root symbols are rendered with a different size.

Is it possible to equalize the size of the two square root symbols?

user000001
  • 248

3 Answers3

9

enter image description here

\documentclass{article}
\begin{document}
  \begin{equation}
    x_{ij} = \frac{
                \sum_{t}{e_i(t)e_j(t)}
             } { 
                \sqrt{\strut\sum_t{e_i^2(t)}} 
                \sqrt{\strut\sum_t{e_j^2(t)}}
             }
  \end{equation}
\end{document}
David Carlisle
  • 757,742
8

Square roots are very sensitive to ascenders and descenders. Just look at the two of them and you'll realize that the culprit is the j in the second one:

\documentclass{article}
\begin{document}

\begin{equation}
  x_{ij} =
  \frac{
        \sum_{t}{e_i(t)e_j(t)}
       }
       {
        \sqrt{\sum_t{e_{i\vphantom{j}}^2(t)}}
        \sqrt{\sum_t{e_j^2(t)}}
       }
\end{equation}

\end{document}

enter image description here

However, it may be a good idea to have \mathstrut in the exponents, so they don't risk touching the vinculum.

\documentclass{article}
\begin{document}

\begin{equation}
  x_{ij} =
  \frac{
        \sum_{t}{e_i(t)e_j(t)}
       }
       {
        \sqrt{\sum_t{e_{i}^{\mathstrut 2}(t)}}
        \sqrt{\sum_t{e_{j}^{\mathstrut 2}(t)}}
       }
\end{equation}

\end{document}

The output is the same.

egreg
  • 1,121,712
2

More of a workaround than a regular answer to your question: using \limits.

\documentclass{article}
\begin{document}
  \begin{equation}
    x_{ij} = \frac{
                \sum\limits_{t}{e_i(t)e_j(t)}
             } { 
                \sqrt{\sum\limits_t{e_i^2(t)}} 
                \sqrt{\sum\limits_t{e_j^2(t)}}
             }
  \end{equation}
\end{document}

enter image description here

Franck Pastor
  • 18,756
  • 2
    the radical signs are really too large, and the use of \limits spaces the numerator farther from the fraction line than desirable. a publisher's copyeditor would probably reject this formulation. – barbara beeton May 12 '15 at 16:24