[SciPy-User] Help!!!!!! having NEW problems with ODEINT

[Kevin Dunn]

On Mon, Jul 25, 2011 at 17:53, Laura Matrajt <matrajt at gmail.com> wrote:
> Laura Matrajt <matrajt <at> gmail.com> writes:
>
>>
>> Kevin Dunn <kgdunn <at> gmail.com> writes:
>>
>> > Hi Laura,
>> >
>> > There's an example in the SciPy documentation on using a Jacobian:
>> > http://docs.scipy.org/doc/scipy/reference/generated/scipy.integrate.ode.html
>> >
>> > This is for the ``ode`` function, not the ``odeint`` function though.
>> >
>> > I've just posted an example on using ``ode`` with coupled ODEs, no Jacobian
>> > over here:
>> >
>>
> http://scipy-central.org/item/13/0/integrating-an-initial-value-problem-multiple-odes
>> >
>> > Hope that helps,
>> > Kevin
>> >
>>
>> Hi Kevin,
>>  the example was good. I now have implemented my Jacobian. Thank you very
> much!!!!!
>>
>
>
> Hi all:
> sorry to bother you again! I implemented the Jacobian as Anne kindly suggested
> to me with the help of Kevin's pointers to the correct webpage AND I increased
> the maximum number of steps as Warren kindly said.
> I am now getting a new message:
>
> lsoda--  warning..internal t (=r1) and h (=r2) are
>       such that in the machine, t + h = t on the next step
>       (h = step size). solver will continue anyway
>      In above,  R1 =  0.1209062893646E+03   R2 =  0.9059171791494E-18

I would find the set(s) of initial conditions that give this warning,
and repeat the integration with a different integrator and/or
different tolerance settings on the integrator. Then compare the
trajectories. If there is negligible difference, then can probably
ignore the warning.

That being said, I've not used the lsoda integrator before, so I have
no idea how serious this warning might be. Which is why I recommend
you try a different integrator also.

Kevin

> It is just a warning, and my code continues to run. But I am really worried
> about this being a bug. The problem is that I am coupling a system of ODE's with
> a stochastic process. Mainly, I simulate a day of an epidemic, stop the
> integrator, change some of the initial conditions stochastically (not just
> randomly, I do follow some rules) and I run the ODE again and so on.
>  I have run this millions of times (and I am not exagerating about the millions)
> and it doesn't produce any warnings, but every now and then (~15 times) it does
> it. I don't know if this is a bug or just that not all of my domain will be good
> for the ODE's...
> If anyone has any suggestion of how to think about this problem, I will really
> appreciate it!!!!!!
> thanks to all the people that replied to me previously, you helped me sooo much
> already!