[Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity

[Ben Abbott]

Follow-up Comment #58, bug #36732 (project octave):

I've pushed a changeset to make testing more convenient ... unfortunately, I
forgot to modify the changelog description :-(

http://hg.savannah.gnu.org/hgweb/octave/rev/94d512d712e3

Ed, I hesitate to change the choice of left/right continuity as this was
decided quite some time ago (several years I think).

The example below may be of interest.


X = [ 2 1 3 2];
Y = [ 9 1 3 10]; 
% These are right-continuos (returns 10 at X=2)
y1 = interp1 (X, Y, 2)
[~, n] = sort (X);
y2 = interp1 (X(n), Y(n), 2)
[~, n] = sort (X, "descend");
y3 = interp1 (X(n), Y(n), 2)
y4 = interp1 (X, Y, 2, "-right")
% These are left-continuous (returns 9 at X=2)
[~, n] = sort (fliplr (X), "descend");
y5 = interp1 (X(n), fliplr(Y)(n), 2)
y6 = interp1 (X, Y, 2, "-left")


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