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[Octave-bug-tracker] [bug #56636] Octave's interp1 does not have the sam
[Octave-bug-tracker] [bug #56636] Octave's interp1 does not have the same rules for when to extrapolate as Matlab.
Mon, 15 Jul 2019 18:10:02 -0400 (EDT)
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Summary: Octave's interp1 does not have the same rules for
when to extrapolate as Matlab.
Project: GNU Octave
Submitted by: crobar
Submitted on: Mon 15 Jul 2019 10:10:00 PM UTC
Category: Octave Function
Severity: 3 - Normal
Priority: 5 - Normal
Item Group: WTF, Matlab?!?
Assigned to: None
Originator Name: Richard Crozier
Discussion Lock: Any
Operating System: Any
This has sort of been reported in bug #42686, but that bug is closed.
The rules for when interp1 performs extrapolation, rather than returning a Nan
outside the domain differ for Octave and Matlab.
In Matlab for example:
x = linspace (0, 10, 100);
y = x .* 10;
yq = interp1 (x, y, 11, 'spline')
In Octave this returns nan.
The Octave docs state "If extrap is the string "extrap", then extrapolate
values beyond the endpoints using the current method. If extrap is a number,
then replace values beyond the endpoints with that number. When unspecified,
extrap defaults to NA. "
This differs for Matlab, where for the 'pchip', 'spline', or 'makima'
interpolation methods, then the default behaviour is 'extrap', but otherwise
the behaviour is the same as Octave where the default is nan, unless extrap is
Personally I prefer the Octave way and think silently extrapolating without
warning the user, or the user asking for it, and having different defaults
depending on the extrapolation method is a bit mad, but it is definitely an
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- [Octave-bug-tracker] [bug #56636] Octave's interp1 does not have the same rules for when to extrapolate as Matlab.,