[Octave-bug-tracker] [bug #50012] ode23 internal interpolation

[Andreas Stahel]

URL:
  <http://savannah.gnu.org/bugs/?50012>

                 Summary: ode23 internal interpolation
                 Project: GNU Octave
            Submitted by: sha1
            Submitted on: Tue 10 Jan 2017 10:38:04 AM CET
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Inaccurate Result
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: Any

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Details:

Recently I ran across a possible problem in the integration/interpolation of
the ode23 solver.
Examine the result of the enclosed script.
The problem shows when working with the derivative of a solution and is most
likely caused by the interpolation to the values given in tspan.
When I change line 157 in the function integrate_adaptive
order --> order+1  or order --> order-1
the results look smooth.
Thus I suspect a minor problem with the piecewise interpolation of the order
used by ode23.

The problems show in version 4.2.0 and the development branch.
The version of ode23 in odepkg does not display the problem.

With best regards

Andreas Stahel



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File Attachments:


-------------------------------------------------------
Date: Tue 10 Jan 2017 10:38:04 AM CET  Name: Test_ode23.m  Size: 838B   By:
sha1

<http://savannah.gnu.org/bugs/download.php?file_id=39422>
-------------------------------------------------------
Date: Tue 10 Jan 2017 10:38:04 AM CET  Name: Test_ode23.png  Size: 29kB   By:
sha1

<http://savannah.gnu.org/bugs/download.php?file_id=39423>

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