Re: LSODE and Dynamics

[geordie . mcbain]

DrakeGis:

A common trick in formulating dynamical systems is to reduce nonautonomous  
systems like ydot(t) = A(y(t),t) to autonomous systems YDOT(t) = B(Y(t)), by 
including the time as an additional dependent variable.  The time satisfies 
the simple ODE tdot(t) = 1.

This is why LSODE and other ODE integrators don't bother providing for 
explicit time dependence.

Hope this helps,

Geordie McBain


On Tue, 30 Mar 2004 03:46 am, DrakeGis wrote:
> Hi,
>   I have a set of ODE's that "explain" a dynamic process. But the
> coefficients of the ODE's are not constant in time. So, I need to change
> their values at each time... the problem is that lsode only take as
> paramaters the initial conditions, the time interval, and the function
> to solve... but is it not possible to send parameters to that function,
> isn't ?
>
> I solve the problem by using a global variable,
>
> function transient = linear(state, t)
>     global MATRIX;
>     transient = MATRIX * state;
> endfunction
>
>   where MATRIX is the coefficient matrix.... but it is not a very elegant
> solution...,
>
> it is possible to have something like this
>
> function transient = linear2(s,m,t)
>   transient = m * s;
> endfunction
>
>
> and somewhere in lsode invocation add the parameter m ???
> Thanks.
>
>    D.
>
>
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