[Numpy-discussion] suggested change of behavior for interp
Wed Jun 5 09:16:12 CDT 2013
The simplest monotonicity test that I've seen is:
dx = np.diff(x)
monotonic = np.all(dx < 0.) or np.all(dx > 0.)
I expect that this is pretty fast, though I haven't tested it yet. If we
want to make checking optional, then I think the default should be to check
with the option to skip the check.
On Tue, Jun 4, 2013 at 9:03 PM, <email@example.com> wrote:
> From: Eric Firing <firstname.lastname@example.org>
> To: email@example.com
> Date: Tue, 04 Jun 2013 15:08:29 -1000
> Subject: Re: [Numpy-discussion] suggested change of behavior for interp
> On 2013/06/04 2:05 PM, Charles R Harris wrote:
>> On Tue, Jun 4, 2013 at 12:07 PM, Slavin, Jonathan
>> <firstname.lastname@example.org <mailto:email@example.com.**edu<firstname.lastname@example.org>>>
>> I would like to suggest that the behavior of numpy.interp be changed
>> regarding treatment of situations in which the x-coordinates are not
>> monotonically increasing. Specifically, it seems to me that interp
>> should work correctly when the x-coordinate is decreasing
>> monotonically. Clearly it cannot work if the x-coordinate is not
>> monotonic, but in that case it should raise an exception. Currently
>> if x is not increasing it simply silently fails, providing incorrect
>> values. This fix could be as simple as a monotonicity test and
>> inversion if necessary (plus a raise statement for non-monotonic
>> Seems reasonable, although it might add a bit of execution time.
> The monotonicity test should be an option if it is available at all; when
> interpolating a small number of points from a large pair of arrays, the
> single sweep through the whole array could dominate the execution time.
> Checking for increasing versus decreasing, in contrast, can be done fast,
> so handling the decreasing case transparently is reasonable.
Jonathan D. Slavin Harvard-Smithsonian CfA
email@example.com 60 Garden Street, MS 83
phone: (617) 496-7981 Cambridge, MA 02138-1516
fax: (617) 496-7577 USA
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