[Octave-bug-tracker] [bug #47013] bug in spline function

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?47013>

                 Summary: bug in spline function
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Fri 29 Jan 2016 05:04:39 PM UTC
                Category: None
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: bug in spline function
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.0.0
        Operating System: GNU/Linux

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Details:

Hi, 

There is a bug in spline. 

For the complete case in function `spline`, when n > 2,

(line 138 ~ 139 in source code)


      g(2:n-1,:) = (a(3:n,:) - a(2:n-1,:)) ./ h(2:n-1) - ...
                   (a(2:n-1,:) - a(1:n-2,:)) ./ h(1:n-2);


should be


      g(2:n-1,:) = (a(3:n,:) - a(2:n-1,:)) ./ h(2:n-1, idx) - ...
                   (a(2:n-1,:) - a(1:n-2,:)) ./ h(1:n-2, idx);


and (line 147~150 in source code)


      d = d(1:n-1,:);
      c = c(1:n-1,:);
      b = b(1:n-1,:);
      a = a(1:n-1,:);


should be


      d = d(1:n-1,:); d = reshape(permute(d, [2, 1]), 1, []);
      c = c(1:n-1,:); c = reshape(permute(c, [2, 1]), 1, []);
      b = b(1:n-1,:); b = reshape(permute(b, [2, 1]), 1, []);
      a = a(1:n-1,:); a = reshape(permute(a, [2, 1]), 1, []);


sincerely,

ChingChuan Chen 




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