# How to find discrete integral given different time intervals.

I want to implement a PID controller and I'm unsure of how to find the integration part. Normally the integral is calculated as $\sum_{n=1}^{t} e_{n}$, where $e_n$ is the sample error at time n. However, this assumes that the time intervals are all the same. In my case the timer intervals are different So how I find the integral ?

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