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

[Marco Caliari]

URL:
  <http://savannah.gnu.org/bugs/?31098>

                 Summary: Incompatible spline behaviour
                 Project: GNU Octave
            Submitted by: caliari
            Submitted on: Wed 22 Sep 2010 07:51:43 AM GMT
                Category: None
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Improvement/Optimization
                  Status: None
             Assigned to: None
         Originator Name: Marco
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.3.51
        Operating System: GNU/Linux

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Details:

Dear all,

while trying to implement a new bicubic.m function, I encountered the
following incompatible behavior with spline.m: when only three Thorsten Meyer
points X (and three values Y) are given, a unique quadratic interpolant should
be constructed. Besides compatibility, this approach improves a lot the
interpolation behavior with strongly not-equispaced X points. Try the
difference with (example taken by Thorsten Meyer)

x = [0,1,20];
y = x.^3;
xx = linspace(0,20,100);
yy = spline(x,y,xx);
plot(xx,yy)

with and without the enclosed patch.

Best regards,

Marco



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File Attachments:


-------------------------------------------------------
Date: Wed 22 Sep 2010 07:51:43 AM GMT  Name: spline.m.diff  Size: 1kB   By:
caliari

<http://savannah.gnu.org/bugs/download.php?file_id=21517>

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