[Octave-bug-tracker] [bug #60748] lsode throws an unexpected and ill-founded error

[David Leipold]

URL:
  <https://savannah.gnu.org/bugs/?60748>

                 Summary: lsode throws an unexpected and ill-founded error
                 Project: GNU Octave
            Submitted by: dleipold
            Submitted on: Mon 07 Jun 2021 09:15:42 PM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Unexpected Error or Warning
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
                 Release: 6.2.0
         Discussion Lock: Any
        Operating System: Microsoft Windows

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Details:

I encountered a strange "inconsistent sizes for state and derivative vectors
error" while composing a large system of odes joining several vector valued
functions.
I could boil the problem down to the (quite constructed) case below: Two
functions that are numerically perfectly identical, proven by assert on a
random vector. The obscure definition of g triggers something in lsodes cores.
I would expect lsode to call f exclusively with numerically valued vectors of
size(x0), so this is a bug for me. Workaround is possible but very nasty -> I
seem to have to un-vectorize the function?


x0=[1,0];
f=@(x) [-x(2),x(1)];%some vector function
slnf=lsode(f,x0,[0,pi]);%correct

g=@(x) circshift(x,1).*linspace(-1,1,length(x));%strange but
xr=rand(1,2);
assert(g(xr)==f(xr)); %they are perfectly equal in 2D

slng=lsode(g,x0,[0,pi]); %error: inconsistent sizes for state and derivative
vectors





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