[Octave-bug-tracker] [bug #35739] discontinuous derivative from spline w/ 3 points and endpoint derivative

[Keith Lindsay]

URL:
  <http://savannah.gnu.org/bugs/?35739>

                 Summary: discontinuous derivative from spline w/ 3 points and
endpoint derivative
                 Project: GNU Octave
            Submitted by: klindsay
            Submitted on: Wed 07 Mar 2012 06:17:29 AM GMT
                Category: Interpreter
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.6.1
        Operating System: Microsoft Windows

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Details:

Hi,

x = 0:.1:2;
pp = spline([0 1 2], [0 0 1 0 0]);
plot(x,ppval(pp,x));

generates a figure with a discontinuous derivative at
x=1, the middle point. The returned piecewise polynomial
has coefs
       0   1   0   0
       0   1  -2   1

while matlab Version 7.11.0.584 returns
    -2     3     0     0
     2    -3     0     1

Could this be looked into please?

Thanks,
Keith Lindsay




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