I have current vs. time, I want to graph total charge vs. time

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Hi all,

So I have a dataset of electric current (y) vs. time (t), recorded at 20kHz. The range of t is 4ms. Plot(t,y) shows the expected change in current over time, and trapz(t,y) gives the area under the curve.

I would like to plot charge (Q) vs. time (t). Naturally, trapz(t,y) gives me the total charge that passed through the resistor over 4ms. However, I want to have a smooth, monotonic plot of Q from t=0 to t=4 (if y was constant, than charge at t=2 would be half of charge at t=4).

I imagine this as something like the following:

Q(x) = trapz(x,y) where x represents a number that moves from 0 to t (from 0-4ms).

I can't seem to put this together in a way that MATLAB understands, any ides would be welcome. I need the input to be (t,y), and the output to be a list of data points that match up with t, perhaps (t,q).

Thanks for your ideas! Stefan