I have a time-series of voltage values recorded in mV every 0.02 ms, stored as a numpy array.
If I do this,
dv_dt = np.gradient(v),
what will the units of dv_dt be? Will it be some multiple of V/s; e.g. mV/s, mV/(0.02 ms), etc?
My understanding is that gradient returns the derivative of the argument passed to it. Is that right?
See this related question.
Watch out for the unit spacing of dt. As noted in the documentation gradient assumes unit spacing of 1 unless you provide the sample distance by the vararg argument. Your case is only correct, if dt = 1 for all datapoints.
You have to define your units by yourself. It is fine to use milliseconds but unless you do not have a good reason for it, I would use SI units (in this case seconds and Volts; which is the same as mV and ms). The gradient will have units of mV/ms or V/s.
In your case np.gradient(v,0.02) will give you the first order difference of the voltage signal corrected with your spacing of the time axis.
dt is the same for all my datapoints -- it's 0.02 ms, like i said in the question statement -- unless i'm misunderstanding you. with the assumption that dt = 1, is that referring to the spacing in the array, as in, every step of one element in the array represents one dt? i'm still not clear on what the units are of the derivative in my case.
np.gradient(v, 0.02), assuming i want to keep the input array itself as it is. the returned array -- the derivative -- is in units of V / s (not mV / s or anything else, which i guess should've been obvious, considering i submitted a dt in ms and a voltage in mV). if you reword your answer to incorporate this, i'll accept it.