Re: Translating ODE from Matlab to Octave

[c.]

Hi,

On 26 Nov 2013, at 15:19, RICHARD Dominique <address@hidden> wrote:

> Hello everybody,
>   I am switching from Matlab to Octave and I got some code that I am not sure 
> how to deal with.
> For example these lines:
> 
> options = odeset('Mass',M);
> f = @(t,y) daesystem(t,y,params);  
> [t,y] = ode15s(f,t,y0,options);
> 
> which I transformed to :
> 
> lsode_options
>       ('Mass',M);

I don't think "lsode_options" has an option called 'Mass', 
have you looked at the help for lsode [1] or at the help for lsode in 
the manual [2] before writing that command?
furthermore "ode15s" is often (although not exclusively) used to solve 
Differential Algebraic Equations (DAE), i.e. ODEs with a singular mass matrix.
From that and from the fact that your function is named "daesystem" I infer 
that 
probably your problem is a system of DAEs.

If this is the case you should not be using lsode but rather daspk[5, 6] 
to solve your problem. 

Otherwise, if your mass matrix is not singular 
you can just redefine 

  f = @(t,y) M \ daesystem(t,y,params);  

to take the mass matrix into account.

> f = @(t,y) daesystem(t,y,params);
> [y,
>       t]= lsode(@(y,t) f, y0, t)

that is not the correct syntax for calling lsode, [1] and [2] will explain how 
to use it.

> 
> which does not seem to run properly.
> 
> I had a look at the Octave notice but besides the definitions, I did not 
> found clear enough examples for me to use.
do these examples [3, 4] help?

> I would be very grateful for any help to get me to the free side of software.

HTH,
c.


[1] type "help lsode" at the octave prompt to see the help
[2] 
http://www.gnu.org/software/octave/doc/interpreter/Ordinary-Differential-Equations.html#Ordinary-Differential-Equations
[3] http://wiki.octave.org/Cookbook#Parametrized_Functions
[4] http://wiki.octave.org/Bim_package#3D_Time_dependent_problem
[5] type "help daspk" at the octave prompt to see the help
[6] 
http://www.gnu.org/software/octave/doc/interpreter/Differential_002dAlgebraic-Equations.html#Differential_002dAlgebraic-Equations