On Thu, May 1, 2014 at 6:00 PM, Yuxiang Wang <yw...@virginia.edu> wrote:
> Thank you for your input! I prefer np.gradient because it takes > mid-point finite difference estimation instead of one-sided estimates, > but np.diff() is also a good idea. Just wondering why np.gradient does > not have something similar, being curious :) > well, according to the docs, the second order diff() is just calling diff twice anyway, so really the same as what you've done with gradient anyway. I suspect it's just that no one bothered to add that to the gradient API. BTW, I think that numy can handle piecewise polynomials (i.e. splines), so depending on the noisiness of your data, a cubic spline fit may give better gradients -- and if your data are noise second order gradients can get *really* noisy -CHB > Shawn > > On Thu, May 1, 2014 at 6:42 PM, Christian K. <ckk...@hoc.net> wrote: > > Am 01.05.14 18:45, schrieb Yuxiang Wang: > >> Hi all, > >> > >> I am trying to calculate the 2nd-order gradient numerically of an > >> array in numpy. > >> > >> import numpy as np > >> a = np.sin(np.arange(0, 10, .01)) > >> da = np.gradient(a) > >> dda = np.gradient(da) > > > > It looks like you are looking for the derivative rather than the > > gradient. Have a look at: > > > > np.diff(a, n=1, axis=-1) > > > > n is the order if the derivative. > > > > Christian > > > > > > _______________________________________________ > > NumPy-Discussion mailing list > > NumPy-Discussion@scipy.org > > http://mail.scipy.org/mailman/listinfo/numpy-discussion > > > > -- > Yuxiang "Shawn" Wang > Gerling Research Lab > University of Virginia > yw...@virginia.edu > +1 (434) 284-0836 > https://sites.google.com/a/virginia.edu/yw5aj/ > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@scipy.org > http://mail.scipy.org/mailman/listinfo/numpy-discussion > -- Christopher Barker, Ph.D. Oceanographer Emergency Response Division NOAA/NOS/OR&R (206) 526-6959 voice 7600 Sand Point Way NE (206) 526-6329 fax Seattle, WA 98115 (206) 526-6317 main reception chris.bar...@noaa.gov
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