[Octave-bug-tracker] [bug #31098] Incompatible spline behaviour

[Thorsten Meyer]

Follow-up Comment #1, bug #31098 (project octave):

I like the new behaviour given by the patch especially because it gives a
continuously differentiable interpolation curve also for not-equispaced x
values (in the case of 3 element input vectors).

for the example below comparing with the exact fit polynomial I get the
following:

pp=[21 -20 0];
polyval(pp, x) - y
ans =

   0   0   0

max(abs((yy-polyval(pp, xx))./yy./eps))
ans =  3.2670

So at least for this example the result is very accurate. (interestingly, in
MATLAB the difference between the spline and the above polynomial gives
exactly zero).

Also the code change only touches the behaviour of spline for 3 value input
vectors as far as I can see and spline still passes its tests.

I would like to push this (attributed to Marco) if nobody objects.

Regards

Thorsten

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