[Maxima] ODEs: rk routing with derivs on rhs
raymond.toy at ericsson.com
Mon Jan 15 15:12:48 CST 2007
>>>>> "Daniel" == Daniel Lakeland <dlakelan at street-artists.org> writes:
Daniel> In my further attempts to understand my differential equations, I
Daniel> tried to use the "rk" routine. I used "? rk" to get info about it but
Daniel> it seems that I am limited as follows.
Daniel> The system is 2 coupled 2nd order ODEs. It's only second order in h,
Daniel> therefore I need an expression for h', h'', and v' for the integrator
Daniel> and h, h', v will be my solution variables.
Daniel> i can write these equations semi-explicitly...
Daniel> h' depends on h, h'' v, v'
Daniel> v' depends on h, h', h'', v
Daniel> h'' depends on h h' v'
Daniel> It seems as though the rk routine is not happy with this, preferring
Daniel> the rhs to be free of all derivatives. (the error I get is something
Daniel> about attempting to take derivative with respect to a number)
It's not exactly clear here, but aren't you supposed to convert your
two 2nd-order ODEs into four 1st order ODEs? Then rk should be able
to solve them.
But I've never used rk before, and I haven't done ODEs in ages.
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