[Numpy-discussion] "Nyquist frequency" in numpy.fft docstring

David Goldsmith d.l.goldsmith@gmail....
Sun Jul 11 18:13:44 CDT 2010


Hi!  I'm a little confused: in the docstring for numpy.fft we find the
following:

"For an even number of input points, A[n/2] represents both positive and
negative Nyquist frequency..."

but according to http://en.wikipedia.org/wiki/Nyquist_frequency (I know, I
know, I've bad mouthed Wikipedia in the past, but that's in a different
context):

"The *Nyquist frequency*...is half the sampling
frequency<http://en.wikipedia.org/wiki/Sampling_frequency>of a
discrete
signal <http://en.wikipedia.org/wiki/Discrete_signal> processing
system...The Nyquist frequency should not be confused with the
*Nyquist rate<http://en.wikipedia.org/wiki/Nyquist_rate>
*, which is the lower bound of the sampling frequency that satisfies the
Nyquist sampling criterion for a given signal or family of signals...*Nyquist
rate*, as commonly used with respect to sampling, is a property of a
continuous-time
signal <http://en.wikipedia.org/wiki/Continuous-time_signal>, not of a
system, whereas *Nyquist frequency* is a property of a discrete-time system,
not of a signal."

Yet earlier in numpy.fft's docstring we find:

"...the discretized input to the transform is customarily referred to as a *
signal...*"

Should we be using "Nyquist rate" instead of "Nyquist frequency," and if
not, why not?

DG
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