bugGNU Octave - Bugs: bug #49427, structure returned by ode solvers...


bug #49427: structure returned by ode solvers invoked with one output is incomplete

Submitter:  Carlo de Falco <cdf>
Submitted:  Mon 24 Oct 2016 10:41:06 AM UTC
Category:  Octave Function Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Matlab Compatibility
Status:  None Assigned to:  None
Originator Name:  Open/Closed:  * Open
Release:  * dev Operating System:  * Any
Fixed Release:  None Planned Release:  None
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Thu 13 Jul 2017 06:47:21 AM UTC, comment #3: 

I'm interested in giving it a try. I've looked a little at it, and have almost made the jump to making my own version of it. Any help on where to start would be great.

Marshall <marsian>
Wed 12 Jul 2017 02:23:29 PM UTC, comment #2: 

sure, it shouldn't take too much effort to implement deval at the moment, are you willing to help with this?

If so, I can send you precise pointers to the current code
where to start from.

Carlo de Falco <cdf>
Group Member
Wed 12 Jul 2017 01:51:40 PM UTC, comment #1: 

I'm interested in having a deval function. Since odeXX is native to Octave now and does have the output form of sol = odeXX(...), it seems like what's there should be enough to extract deval from the existing functions: It already interpolates internally.

Marshall <marsian>
Mon 24 Oct 2016 10:41:06 AM UTC, original submission:  

The ode solvers in Matlab can be called with two main different
forms for the output

[t, x] = odeXX ( ... );


out = odeXX ( ... );

the second form does not merely aggregate outputs in one
structure but triggers a completely different behaviour of the

The idea is that with the second form the solver advances until
the end of the timespan (or passed it) and does not care of
evaluation of the state at intermediate timesteps.

The output structure "out" contains all data that can be fed
to "deval" to evaluate the solution at any time point between
tspan(1) and tspan(end) to the maximum possible order of
accuracy consistent with the solution method used.

We don't have deval in Octave at the moment and I cannot find
documentation of the actual fields of the output structure in
matlab, so I think we don't need to copy those fields exactly.

On the other hand here is the list of data we would need to do
interpolation as a post-processing step (at least for explicit runge kutta):

  • times selected by the adaptive selection algorithm and state evaluated there

  • order of the method (to select interpolation algorithm)

  • name of the method (to select location of  intermediate "stages")

  • derivatives at intermadiate "stages"

Carlo de Falco <cdf>
Group Member


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