# Problem with \sum subscript

When I use the code below the subscript j appears to the side of the sum symbol, not underneath. Has anyone got any idea what I'm doing wrong?

$$\Delta{t}\leq\left[{C_i}\over{{\sum_{j}}{\frac{1}{R_{ij}}}}\right]_{min} \label{eq:stability_criteria_3}$$

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Please put your code in Code Samples (the '{}'-button) to make it more readable – Didii Jul 23 '12 at 13:56
Here is the same issue in another environment. Solution is the same: tex.stackexchange.com/questions/3262/… – Didii Jul 23 '12 at 14:03
In LaTeX, rather use \frac{<num>}{<denom>} than <num>\over<denom>. – Werner Jul 23 '12 at 14:18

Consider using \limits as in the following:

    $$\Delta{t}\leq\left[{C_i}\over{{\sum \limits_{j}}{\frac{1}{R_{ij}}}}\right]_{min} \label{eq:stability_criteria_3}$$


(Doesn't this make this ugly though?)

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Adding a \displaystyle does the job.

$$\Delta{t}\leq\left[{C_i}\over{{\displaystyle \sum_{j}}{\frac{1}{R_{ij}}}}\right]_{min} \label{eq:stability_criteria_3}$$

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The \displaystyle instruction will change both the size of the summation symbol and the default placement of the limit(s) of summation. – Mico Dec 20 '12 at 13:24