[Octave-bug-tracker] [bug #49427] structure returned by ode solvers invoked with one output is incomplete

[Carlo de Falco]

URL:
  <http://savannah.gnu.org/bugs/?49427>

                 Summary: structure returned by ode solvers invoked with one
output is incomplete
                 Project: GNU Octave
            Submitted by: cdf
            Submitted on: Mon 24 Oct 2016 12:41:06 PM CEST
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Matlab Compatibility
                  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:

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


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


or


out = odeXX ( ... );


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

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"













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