From help-octave-request at bevo dot che dot wisc dot edu Thu Sep 12 02:05:35 2002
Subject: Re: Help with ODE solver
From: Douglas Eck <doug at idsia dot ch>
To: Marco Antoniotti <marcoxa at cs dot nyu dot edu>
CC: help-octave at bevo dot che dot wisc dot edu
Date: Thu, 12 Sep 2002 09:05:18 +0200

Hi Marco,
My experience is that it's better to break down the integration into
intervals. Also, if you later need to speed up your code some, it can
be much faster to write the xdot = f(x,t) as a compiled .oct file.



Marco Antoniotti wrote:
> Hi
> 
> I am using the LSODE solver for my research and now need to do the
> following.
> 
> At a time t_i, I need to change the value of one (or more) of the
> variable(s) involved.
> 
> I think I understand I have two avenues to follow to achieve this
> goal, but, given my inexperience with Octave (and/or Matlab) I don't
> know which is the best one.
> 
> 1 - I could insert a specific test in the derivative function
> 
>   function xdot = f(x, t)
>     xdot = zeros(rows(x), 1);
> 
>     if (t == t_i)
>        ## set x(k) to M
>     endif
> 
>     xdot(1) = ...
>     ...
>     xdot(n) = ...
> 
>   endfunction
> 
> 
> 2 - I could break down the integration into intervals and set the
>     variable value between integrations.
> 
> I'd like some comments about what would be the "best" (for an
> approrpiate definition of "best") way to achieve this goal.
> 
> Thanks
> 


-- 
Dr. Douglas Eck, http://www.idsia.ch/~doug
Istituto Dalle Molle di Studi sull'Intelligenza Artificiale (IDSIA)
Neural Networks, Rhythm Perception and Production, Dynamical Systems



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